Archives for category: fish


The Pufferfish is considered the second deadliest vertebrate in the world, after the Golden Poison Frog. The common image we have of this creature is that it inflates when threatened. I have kept these fish in an aquarium, and in my experience they rarely puff out in captivity.

What makes the Pufferfish, also called the Fugu so popular is the lethal toxin in its liver, skin and the ovaries, and the fact that the Japanese treat it as a delicacy. Pretty ironic I guess? By the way it is extremely expensive and prepared only by trained, licensed chefs who, like all humans, occasionally make mistakes.

Image: blogs.bootsnall.com

Almost all pufferfish contain tetrodotoxin, a substance that makes them foul tasting and often lethal to fish. To humans, tetrodotoxin is deadly, up to 1,200 times more poisonous than cyanide. The toxin paralyzes the muscles, including the muscles in our diaphragm, which is essential for breathing. The victim eventually dies of asphyxiation. There is enough toxin in one pufferfish to kill 30 adult humans, and there is no known antidote. Tetrodotoxin has been isolated from widely differing animal species, including western newts of the genus Taricha (where it was formerly termed “tarichatoxin”), pufferfishtoads of the genus Atelopus, several species of blue-ringed octopuses of the genusHapalochlaena (where it was called “maculotoxin”), several sea stars, certain angelfish, a polyclad flatworm, several species of Chaetognatha (arrow worms), several nemerteans (ribbonworms) and several species of xanthid crabs.


Tetrodotoxin molecule


Image: gastroville.com

Negative aspects aside, Puffer Fish makes cute companion.

Of course, don’t go around scaring puffer fish because a puffer fish could only perform a limited number of inflation in its life.

Image: animals.nationalgeographic.com

When a Pufferfish is threatened, it will pump itself up by taking 35 gulps or so in the course of 14 seconds. Each gulp draws in a big load of water thanks to some peculiar anatomic changes in the muscles and bones. The entire fish balloons as it continuously takes water into its stomach.

The stomach expands to nearly a hundred times its original volume, and the fish’s spine, already slightly curved, bends into an upside-down U shape, and all other internal organs become squeezed between the fish’s backbone and its rapidly expanding stomach. Meanwhile, the fish’s skin is pushed out, obscuring most of the puffer’s features-http://divingintaganga.blogspot.com/2010/09/how-and-why-pufferfish-inflate.html

Image: Sally J. Bensusen. American Museum of Natural History.

Sometimes they have difficulties expelling water from their stomach, and hence they actually risk dying every time they inflate. I guess we should record a default video showing one individual inflating itself on a public website to prevent curious divers/swimmers/fishers going around harming more Pufferfish. Pufferfish belong to family Tetraodontidae is a family of primarily marine and estuarine fish of the order Tetraodontiformes. The family includes many familiar species, which are variously called pufferfishpuffersballoonfishblowfishbubblefishglobefishswellfishtoadfishtoadies,honey toadssugar toads, and sea squab. They are morphologically similar to the closely related porcupinefish, which have large external spines (unlike the thinner, hidden spines of Tetraodontidae, which are only visible when the fish has puffed up). The scientific name refers to the four large teeth, fused into an upper and lower plate, which are used for crushing the shells of crustaceans and mollusks, their natural prey.

With all of this, many people still consider Fugo to be a delicacy , especially in Japan.


info:
http://www.aquaticcommunity.com/predatory/pufferfish.php
http://en.wikipedia.org/wiki/Fugu
http://divingintaganga.blogspot.com/2010/09/how-and-why-pufferfish-inflate.html

A word on aquarium science
Fishkeeping is a subjective science. I say subjective, because there are many ways to accomplish the same task. I say science, because there are some hard and fast rules that must b e adhered to. That said, we hope to give you information on one o the ways to maintain a successful aquarium. It’s not the only way. It may not even be the best way. But it a way that is proven and works. We also hope to provide you with the science behind aquariums to make educated decisions about your aquarium.
Types of Aquariums
An aquarium is a container that houses aquatic life, whereas a terrarium is a container that houses live plants and animals. 
A wide variety of commercially available aquariums are designed specifically for marine organisms.  The large number of styles, shapes, and sizes will fit just about anyone’s tastes.  Designs include freestanding rectangular tanks, hexagon tanks, curved front tanks, and models that resemble a coffee table.  Many manufactures will build a custom design upon request. Regardless of shape, there are two basic building materials, Glass, and acrylic. There are advantages and disadvantages o each.
All Glass Aquariums
The most common type of aquarium is an all glass tank.  Capacity will vary from 2.5 gallons to hundreds of gallons.  All glass tanks are constructed of plate glass, held in place by silicone gel.  The thickness of the glass increases as the size increases.  The tank is then finished with a molding to protect the sharp edges of the glass.
A glass aquarium may be used for either saltwater or freshwater setups.  Never use a metal frame aquarium for a marine setup- as it will react with the salts in the water and become toxic.  All glass aquariums are relatively cheap, readily available, and long lasting.  Some of the disadvantages are the weight of the larger glass aquariums and difficulty in moving them around.
When you purchase an all glass tank- be sure to inspect it for cracks, and closely inspect al the silicone seals for signs of poor workmanship.  And irregular seal along an inside joint could eventually lead to a leak.
Acrylic Aquariums
Acrylic plastics are strong and can be molded into many shapes and contours.  Any acrylic pieces are joined with special acrylic cement.  Most aquariums of this variety feature curved fronts, curved corners, and colored backs.  Many include built in filtration systems, as well as other features.
Some advantages of acrylic aquariums re the fact it’s relatively lightweight.  A 100-gallon acrylic tank weighs much less than the glass counterpart.  Modern acrylics are very scratch resistant.  Although this is also a disadvantage.  Acrylic can be scratched by many cleaning devices and decorations.  But many commercial cleansers are available to prevent this.  Another disadvantage with acrylic tanks is the initial high cost of getting an acrylic tank.
SIZE
Determining the proper size of the aquarium depends on the number and type of fish, the available space and economic constraints.  To the new marine tank hobbyist, the largest tank one can afford is best.
Marine aquariums should be larger than their freshwater counterparts.  Whereas a 10-gallon tank can be perfectly suitable for freshwater tropical fish, the same size can be quite vexing to the new saltwater hobbyist.  Many species of marine fish are very territorial and require large spaces to coexist peacefully.  Since an aquarium is an enclosed body of water, this small volume will foul more quickly.  Marine fish tend to be more sensitive to this, and a larger aquarium is more forgiving to these complications.  As a general rule- it I best to begin with a rectangular tank for 45 to 55 gallons.  You should try to get a tank with the maximum surface area.  So rather than a tall tank, go for a tank with longer width and length.
It is quite possible to utilize a small tank for a marine tank.  But because of the rapid water quality changes that may occur in a smaller tank, it is not recommended.  Select the largest tank you can afford. This is one of the most important decisions and will determine your future success.
Tank Shape
You should also give careful consideration to the shape of your aquarium.  The various available shapes have a direct effect on the marine environment.  Long tanks provide greater surface area and reduced depth.  The greater the surface area of the tank, the better the gas exchanges at the surface- and therefore the more rapid the dissipation of carbon dioxide and the absorption of oxygen.  Certain aquarium shapes can appear pleasing to the eye, but may not have the environmental advantages offered by more standard designs. 
As a general rule- if two aquariums have the same gallonage, but differ in their surface area. Always choose the greater surface area.
Aquarium Weight and Placement
A very important consideration in deciding the size of an aquarium is its total weight full.  This includes water, pumps, filters, and decorations like live rock, gravel, etc. 
An aquarium can be placed on a piece of furniture if it is capable of supporting the weight.  Keep in mind that saltwater eventually will eventually spill on the surface of the furniture.
It I most desirable to purchase an aquarium stand for your tank. It will support the weight as well as resist any damage due to the corrosive nature of saltwater.
You must also be certain that the floor where the aquarium setup is placed can support such a weight.  For example- a 200-gallon tank filled with water, not including gravel, decorations, etc. will weight 1700 pounds. Complete with decorations and gravel, this jumps to over 1 ton.
Setting Up the Aquarium
Once you have purchased the basic equipment it is time to set up your aquarium.
 
Tank Location
Where the aquarium is placed is a matter of personal preference.  It makes a beautiful focus in a living room, den, bedroom, or any other room.  Larger aquariums can be placed as an attractive room divider.  Wherever you decide to situate the aquarium, it is important to have easy access to multiple wall outlets to minimize the use of extension cords.
The aquarium should not be placed either in an area subject to cold drafts or in one that is excessively warm.  Do not place the aquarium too close to a radiator, air conditioner, or directly in front of a window hat receives direct sunlight.  While several hours of sunlight are beneficial to marine aquariums, strong sunlight can promote excessive algae growth as well as overheating small aquariums.  This is particular dangerous in the summer months.
The selection of an aquarium and stand should also take into account the structural integrity of the building or dwelling.  Always make sure the aquarium is level to avoid any stress on the walls of the tank.
Substrate
The substrate (material to cover bottom of aquarium) should be selected carefully.  Some bottom materials used in freshwater aquariums are not suitable for use in marine aquariums.  Freshwater aquariums often use quartz gravel, epoxy covered rocks, or other dyed decorations.  These materials may become toxic with the interactions of seawater in a marine aquarium. 
Only substrates with a calcareous composition should be used for marine aquariums.  These are the only types with any ability to buffer the water. The most commonly available appropriate substrate includes natural crushed corals, limestone, dolomite, or crushed oystershell.  A combination of these can be used to create a natural habitat.
Aquarium bottom materials are essential for proper biological and mechanical filtration when an undergravel filter is used.  Large size grains of substrate should be avoided, as they inadequately perform mechanical and biological filtration of the water. They also have substantially reduced surface area compared to smaller size particles.  This means there is less area for the beneficial nitrifying bacteria to grow on.  On the other hand, very small grains, such as sand must never be used to cover and undergravel filter bottom.  Sand will rapidly clog an undergravel filter and prevent uniform flow though this plate.  The general recommendation is to select a grain size of 4 to 5 mm.
Various substrates are suitable for use in marine aquariums and include a mixture of shells crushed coral and dolomite.  Sand should never be used to cover the aquarium bottom. Sand will rapidly clog undergravel filters and prevent a uniform flow of water through the filter plate. The general recommendation is to select a grain size of 3-5 millimeters (mm). If no undergravel filter is used, virtually any size of calcareous material can be used to cover the aquarium bottom.
Amount of Required Substrate
The amount of material for an aquarium is mainly dependent on whether you are using an undergravel filter. It is highly recommended that you include an undergravel filter as standard equipment for your first aquarium.
With an undergravel filter recommended depth of bottom material is 2.5 to 3.0 inches (6.S-7.5 cm). This will ensure that you have ample material for proper filtration through your biological filter. You may make the bottom material deeper. But do not make it less that the stated guideline.
In aquariums without an undergravel filter, a shallow layer of substrate is all that should be used to cover the bottom, with a depth of not more than 1/2 to 1 inch (1.2-2 cm) of substrate. The size substrate in this situation is not as critical as with aquariums with undergravel filtration.
Without an undergravel filter. The bottom material depth must be restricted to minimize the possibility of anaerobic bacterial activity. These bacteria develop in filter beds where there is restricted water flow to carry dissolved oxygen.
Without a constant water flow through a filter bed, the substrate favors the growth of anaerobic bacteria, producing toxic gases such as methane and hydrogen sulfide. Both of these gases, even in very low concentrations, are poisonous to marine animals.
Conditioning Water
Unconditioned municipal water is unsafe to use in an aquarium. ”Water conditioning” means different things depending on the context. Here the phrase refers to the detoxifying of municipal water that contains toxic chemicals, the most serious being chlorine and chloramine. Tap water can also contain toxic metal ions such as copper, aluminum, or other dissolved materials in concentrations that can be toxic to aquatic life. This can be a particular concern in areas where water districts add copper to water reservoirs during the summer to control algae.
 All municipal water should therefore be treated with a good-quality water conditioner prior to mixing with sea salts. These conditioners are available as a liquid or powder. When used according to instructions, they will destroy chlorine and chloramines within minutes. Some conditioners will also render metallic ions nontoxic if they are present in your tap water. Some brands of synthetic sea salts contain a water conditioner that will destroy chlorine and chloramine while the sea salts are dissolved. Water conditioners should al-ways be used whenever adding new tap water to the aquarium.
 Decorating Your Aquarium
The marine aquarium can be decorated or aquascaped in various ways to simulate undersea habitats. You may decide to design a coral reef environment. A reef and lagoon area, or a rocky deep-sea environment. It will be helpful to obtain books or magazine articles with color photos of coral reefs to become familiar with the appearance of the reef environment With such photos as a guide you will be able to construct a more natural and authentic-looking aquarium.
Coral and rock can be arranged to simulate a natural environment and include ample hiding areas, ledges, and crevices for the aquarium fish.
Placement of the rock and coral should not be so complex that it will be difficult to remove uneaten food or detritus during maintenance-
It is always best to start the arrangement of large pieces of coral rock or other rock at the back of the aquarium. You can build up a wall of rock, then place a few select pieces of coral on some of the ledges. Work towards the front of the aquarium, arranging coral, rock, and decorations to allow hiding areas, but also to leave ample swimming room for the fish.
Various types of natural decorations are avail-able to decorate a marine aquarium, including several types of rock such as lava rock, coral rock. There are also decorative items that are replicas of natural coral, sea fans, gorgonian, and sponges.
Living macroalgae make beautiful additions to the marine aquarium; in addition to being decorative they serve other purposes, including removal of nitrogen compounds.
It is important to note that not all rock is safe for aquariums. Many contain quantities of soluble metal salts that can quickly kill marine animals. Only rock that has been purchased should be used in a marine aquarium. Do not use any rock that has been collected unless you can be assured that it is nontoxic. All rock should be washed well to remove any sand or dirt before adding to your.
Natural Coral
The most frequently used decorative item in a marine aquarium is coral. Various types are avail-able, including brain coral, finger coral (Porites), staghorn coral, and organ pipe coral.
Any purchased coral should be soaked in fresh water prior to use to ensure that all organic material has been cleaned before placement in the aquarium. Coral from pet shops is often pretreated and cleaned prior to sale. Such coral can be used after it has been rinsed to remove any dust or other materials that have adhered to the coral skeleton.
However, it is still recommended that you subject it to a special cleaning process. This ensures that all organic material has been removed from the coral prior to placement in the aquarium.
First, the coral should be p]aced in a non-metallic bucket with fresh water to completely cover the coral for at least 72 hours in a warm area.
If the water is still clear after 72 hours and no odor is discerned, the coral can safely be re-moved, rinsed, and added to the aquarium. However, if you notice a film on the water, a cloudy appearance to the water, or a bad odor, remove the coral pieces, rinse well and proceed as follows.
Place the coral in a bucket using 8 ounces (0.2 L) of household bleach for every gallon
Algae Growth in New Aquariums:
Once your aquarium has been in operation for a week or more you will undoubtedly begin to notice a brown color on the substrate, rock, and coral.
This process is quite normal and is the first stage in the establishing of the aquarium. The brown color is primarily due to the Growth of microscopic golden-brown algae called diatoms. Since they require very little light to develop and are tolerant of various types of water conditions, they are able to reproduce rapidly. However, if ample light of the correct intensity is provided for at least eight to ten hours daily, you will notice the development of green algae that will replace the growth of diatoms. This will usually begin within several weeks to one month, and will first be noticeable on rock or coral closest to the light source. With the correct conditions, the green algae will slowly replace the brown algae and red algae, if they also have grown during the first few weeks.
If growth of green algae does not begin within a month, the cause may be inadequate light intensity or duration, water quality problems, and not enough green algae cells to start the growing process. Green algae cells are usually introduced with the fish or invertebrates. If the light and water quality appear to be correct, it may be necessary to obtain a small culture of algae from your retailer.
All that is needed is a small amount of green algae removed from a rock or glass and placed in the aquarium.
WATER AND WATER QUALITY
Fish and other marine organisms are directly influenced by the chemical, biological, and physical characteristic of their environment.  The water around coral reef habitats is chemically stable because of the large volume of water, the constant currents, wind, and other factors that help maintain the relative uniformity of the oceans.  As a result, reef organisms are not subjected to wide fluctuations in the chemical and physical characteristics of  seawater.  When there is a change- it is usually short enough that the animals are not adversely affected.
The situation in the aquarium is much different.  The aquarium water is not subject to constant renewals as in the ocean.  In contrast to a coral reef, the aquarium water is subject to extensive alterations after the introduction of marine organisms. The alteration of water quality is due to the buildup of chemicals that originate from various biochemical processes, most notably the metabolic activities if fish, invertebrates and algae.  If these chemicals are permitted to accumulate to concentrations beyond which aquatic animals can tolerate , the survival of the animals is in jeopardy.  The toxicity of many of these compounds is such, that even short exposure to low concentrations may be lethal.  That is why it is so crucial to test water regularly and perform periodic water changes.
Natural Seawater
Seawater is a complex medium of numerous chemical compounds, both organic and inorganic.  Sodium Chloride, is the most abundant element in seawater.  This is the same as common table salt.  he other major components are magnesium chloride, magnesium sulfate, and calcium carbonate.  In smaller concentrations, other trace elements are present.  Some of these include molybdenum, selenium, cesium, vanadium, zinc, iodide, and iron.  Though these elements are low in concentration, they are required for the biological processes of many plan and animals organisms.
Marine aquariums can be filled with either natural seawater or freshwater plus a synthetic seawater mixture.  Natural seawater must first go through a conditioning process before being used in your aquarium.  Natural seawater contains many planktonic organisms.  Most of these are microscopic.  These are both plant (phytoplankton) and animal(zooplankton).  If the water is not properly conditioned, then the death of these organisms could cause radical changes to the water quality.  Secondly, naturally collected seawater is a vector for disease.  Many parasites, and diseases may be introduced, as well as planktonic forms of animals that are potentially harmful.  For the new aquarist, it is far easier to use synthetic seasalt.
If you do collect natural seawater, then it should be collected away from inshore areas, or inner bays.  This is to ensure the best water quality and least amount of urban pollution and runoff.  Nearshore areas can be polluted by from fertilizer runoff, sewage, toxic metals, insecticides, and other pollutants.  Inshore waters may also contain a high level of suspended particles, mostly from storm drain run off, and erosion from shoreside developments.  And even freshwater rivers flowing into the ocean. Collect all seawater in non-toxic plastic containers with secure lids.  Once collected, you should leave the containers in a dark room, with the lid on for 3 weeks.  This allows any harmful organisms to die off and the toxins to dissipate.  After storage, you will notice a layer of detritus from the dead microorganisms on the bottom.  This should not be added to the aquarium.  Instead, siphon off the top layers of water and add to aquarium.  After addition to the aquarium, you should always monitor pH, ammonia, nitrite, and nitrate, and increase aeration to disperse new water evenly.
Synthetic Seawater.
The invention of synthetic sea salt mix for keeping marine fish and invertebrates in aquariums was a major achievement that enabled anyone anywhere to set up a marine aquarium.  It allowed the convenience of preparing seawater by mixing synthetic sea salt with a freshwater source. There are many formulas available today that are of very high quality and mach natural seawater very closely.  Experience has demonstrated that these synthetic seasalts can be a superior choice for supporting life.
The major advantages of preparing synthetic sea water are that it is free of pollutants and microorganisms that could transmit disease or foul the water, there is no need for storage for extra seawater, and the preparation can be used a short time after mixing.
Various commercial mixes are available for making seawater..  The salt is simply mixed with an appropriate amount of tap, DI, or RO water, allowed to mix until thoroughly dissolved, and then salinity adjusted until at appropriate level.  Using this method, fish can be introduced into a new aquarium in as little as 12 hours. 
Water Parameters
Once the fish are introduced to the aquarium water, it will begin to undergo a series of chemical changes, not all of, which are conducive to the support of aquatic life.  It is therefore crucial to ensure that a high quality of water quality is maintained.  Marine animals are extremely sensitive to water deterioration and are not as tolerant as many species of freshwater fish to poor water quality.  Without a thorough understanding of the required water quality parameters you will not succeed as a saltwater aquarist.  There are a number of parameters that are critical.
Temperature
Most aquarists will be stocking their aquariums with fish and invertebrates from coral reef habitats.  Living coral, and other invertebrates, and fish are extremely sensitive to rapid temperature fluctuations.  Since fish and inverts are cold blooded, they are directly affected by temperature, which affects their activity, feeding behavior and immunity and other metabolic functions.  For example, the higher the temperature, the greater the need for food.; but this causes an increase in the metabolic waste products in the water.  If there is too low a temperature, the activity levels of the animals slows, and a reduction in growth rate, and sensitive animals like corals will die.  Such problems, especially the buildup of wastes, are inconsequential on the coral reef, but are deadly within an aquarium.
Temperature also affects the amount of dissolved gases that directly affect the marine organisms.  At high temperature, less oxygen will dissolve in water.  This reduces the capacity of the aquarium and the waters ability to provide oxygen to the fishes respiratory system.
The temperature of an aquarium should be constant and maintained within an acceptable range. The ideal range for many marine animals is 77 to 82 ˚F (25-28˚C).  This range takes into account the majority of marine animals that would be kept in an aquarium. However for the majority of aquariums stocked only with fish, the recommended range would be 77 to 79 ˚F (25-26˚C).  Certain animals will require either a lower temperature or a higher one.  It is always best to research any specimen before introducing it into an aquarium.
pH
The pH of water is a measure of acidity or alkalinity.  The pH ranges from 0 to 14, with 7 being a neutral point.  Above neutral, pH 7, water is alkaline,.  Below pH7, water is acidic.  Because of the complex chemistry within an aquarium, the pH may undergo major shifts.
In nature, the pH of ocean water is usually 8.0 or above, varying with the locality.  It is recommended that seawater in the marine aquarium be maintained within the range of 7.8 to 8.3, depending on the type of marine organisms maintained.  A pH of 8.0 to 8.3 is the generally accepted value for an aquarium with both invertebrates and fish.
Changes in the pH of the water are caused by various chemical reactions and the presence of chemical compounds that slowly accumulate.  Several factors in an aquarium contribute t changes in pH, including the nitrification process, the concentration of carbon dioxide and the amount of natural buffers.
The nitrification process releases acids that react with bicarbonates to neutralize the acids.  Without bicarbonates and carbonates to buffer the water, it would slowly become acidic, endangering the animals.  Buffers restrict a great change in the pH of a solution.  Water in the ocean, which is naturally buffered, has great pH stability.  Many synthetic seawaters contain sufficient buffers for the new aquarium.  The type and quantity of substrate can also play a role in maintaining the pH of a captive marine system.  Carbon dioxide is also a source of acid in an aquarium.  Aquariums with inadequate circulation and aeration can buildup excessive amounts of carbon dioxide.
The general trend of pH in a stocked aquarium is a continual decrease towards more acidity.  Gradual declines are not harmful, but the marine hobbyist must be aware of pH changes to ensure that it does not fall outside of the acceptable range.  Various types of substrates will help to buffer the water and maintain the pH.  However, one time use compounds will become exhausted and have to be replaced.
The pH of water can be measured with inexpensive kits.  A few drops of an indicator chemical is added to a sample of aquarium water in a test vial.  The color of the sample is compared to a color chart that indicates the pH of the water.  This test should be run weekly for established aquariums, and every day for new aquariums.  A pH kit is essential for any aquarium.
Dissolved Oxygen
Aquatic marine mammals in nature inhabit an environment with an abundance of dissolved oxygen.  In aquariums equipped with proper filtration and aeration, sufficiency of dissolved oxygen is seldom a problem.  It is therefore generally unnecessary to test oxygen levels on  regular basis in an aquarium.  However, it must be understood that as the temperature of an aquarium increases, the levels of dissolved oxygen in the water decrease.
Ample concentration of dissolved oxygen is also required for the normal function of the biological filter bed bacteria.  The nitrifying filter bacteria are a major consumer of dissolved oxygen in an aquarium.  In general, it is recommended that dissolved oxygen saturation e at near saturation levels.  To avoid a low DO problem, avoid overcrowding, overfeeding, and overcrowding situations.
Specific Gravity and Salinity
The specific gravity (density) is the ratio of the amount of total dissolved solids water when compared to pure water.  Pure water has a specific gravity of 1.000.  As more salts are added to this volume, the specific gravity increases.
The amount of salt in a marine aquarium is determined by the use of a hydrometer.  This instrument is made of a sealed glass tube with an internal scale.  The hydrometer is weighted at the base and floats freely when placed in the water. Higher quality hydrometers are calibrated to seawater at a known temperature, usually 59˚F (17˚C. If a reading is taken at any temperature other than 59˚F (17˚C), the reading must be corrected by a table using a table of conversion factors. Such tables also give the salinity values.  The temperature must be taken into account, as seawater expands and becomes less dense as temperature rises.
Other hydrometers are available that are standardized at different temperatures and are more appropriate for the use in marine aquariums. A correction I not required since they have been calibrated for the ideal temperature range for fish and invertebrates.  Another variety of hydrometer is constructed from a narrow plastic chamber and it has a dial.  A water sample is collected and fills the chamber and the dial indicates the specific gravity.  When used according to instructions, a correction table is not necessary.  This is the easiest method to test specific gravity in your aquarium.
Marine aquarists can determine the correct density (specific Gravity) by use of a hydrometer that has been calibrated for use in a marine aquarium.  Two methods are suggested: (1) Reading in the aquarium.  Turn off the filters and aeration devices to prevent movement.  Then carefully place the hydrometer into the aquarium and wait until the vertical movement stops.  Read the scale at the lowest point where the water level crosses the hydrometer scale.  Record times, date and temperature along with your density observation.  (2)  Fill a clear cylinder with a water sample.  Carefully place hydrometer into sample and wait until all vertical movement is stopped.  Read the scale as indicated above.  Record vales.
Fish and invertebrates should be maintained in water with a specific gravity of 1.020 to 1.024 at temperatures of 77 to 80˚F (25-26˚C).
Specific Gravity checks should be conducted every week or two.  As water evaporates, the specific gravity will increase, requiring replacement with conditioned tap water.  If the specific gravity drops below the normal range, you will need to add small amounts of seasalts.  This must be done with caution, as to avoid a rapid change in salinity.
Nitrogen Compounds
Various nitrogen compounds formed in the marine aquarium are generated from biochemical processes including the breakdown of proteins and waste products from marine animals  The principal nitrogen products of concern to the marine hobbyist are: ammonia, nitrite, and nitrate.
Ammonia
Ammonia is the most toxic product formed in water.  It originates from the decomposition of nitrogen-containing organics such as plans and food.  Sources for ammonia in the aquarium are the fish, other organisms, and decaying food.
Ammonia exists in two chemical forms in water; an unionized form (NH3) and an ionized form (NH4+). The combination of these two forms termed total ammonia.  Both exist in water, but the proportion of each type is dependent on the pH, temperature, and other factors.  The unionized form is extremely toxic to marine animals, both fish and invertebrates.  The higher the pH, the higher the concentration of unionized ammonia.
Chronic concentrations of ammonia in aquariums indicate that there is a serious problem that can be related to various factors, including overcrowding, filter malfunction, or overfeeding.  Fully functional and operational aquariums should have no detectable traces of ammonia.
Ammonia can be easily detected using commercially available test kits.  Some kits will express the results as ion, while others will express it as ammonia-nitrogen. As a general recommendation, the unionized form of ammonia must not exceed 0.01 mg/l in marine aquariums.  Always follow the manufacturer’s instructions exactly to obtain the correct readings for ammonia.
Nitrite
During development of nitrifying bacteria in the filter bed, the bacteria will transform ammonia into another form of nitrogen called nitrite.  Nitrite is an intermediate step in the nitrogen pathway in the conversion of ammonia into nitrate.  The highest concentrations occur during the initial establishment of the filter bed.  Once the bio-filter has been established, it is often impossible to detect levels of nitrite.  Though nitrite is less toxic than ammonia, it is still toxic to marine organisms. This is because it binds with blood cells, which will prevent the normal uptake of dissolved oxygen.
Nitrate
Nitrate is formed from the chemical conversion of nitrite in the marine aquarium.  It is far less toxic than nitrite and ammonia.  Recent research has shown that nitrate is harmful to marine invertebrates, and may contribute to poor health among fishes.  In fishes, long term exposure to levels of nitrate will impair growth, and longhorn survival.
It is recommended that nitrate not exceed 10 mg/L(ppm), and preferably should not exceed 5mg/l (ppm) for invertebrates.  The lower levels can often be difficult to obtain in many aquarium systems. 
   
Nitrogen Pathway.
A new fish tank is a sterile environment.  It has no beneficial bacteria, and nor harmful bacteria.  No animal wastes, no decaying food, etc.
As wet set up the aquarium, we slowly introduce these facets into the formula.  A freshwater fish produces ammonia (NH3) as its primary nitrogenous waste product.  This ammonia is excreted via the gills and the fishes urine.  The fish also excretes solid wastes via feces.
Ammonia, NH3 is toxic to fish.  It can cause surface burns to their skin, and causes respiratory complication.  It is also able to ionize into NH4+, or ammonium.  Ammonium occurs in highest quantities in a tank with a pH over 7.0.  In a pH less than 7.0 the levels of ammonium re reduced. But the ammonia is still there!
This ammonia will build up to toxic levels unless it is removed.  That is where our filtration comes in.  We aid in the removal of ammonia via the different methods of filtration.  Chemical filtration, is a carbon filter or an ion exchange resin filter (like Chemipure).  This kind of filter removes many of the dissolved organics from the water.  A biological filter is one that supports growth of bacteria that break down some of the fish wastes,  These bio-filters usually have a material that allows millions of  microscopic bacteria to flourish.  These bacteria oxidize and convert the ammonia and ammonium into nitrite.  These bacteria are called Nitrosomonas. 
Nitrite, NO3 is also toxic to fish.  In very small concentrations  it will cause respiratory distress and make fish susceptible to invading disease. Nitrobacter bacteria consume this nitrite.  They convert it into Nitrate.  NO4. 
Nitrate is relatively harmless to freshwater fish in normal concentrations.  There are no bacteria in standard freshwater aquarium set ups that convert nitrate into anything else.  So it must be removed in some manner.
The most common way to remove nitrate is through regular partial water changes.  This physically removes the nitrates from the water.  This also has the additional benefit of replenishing many of the nutrients and minerals taken up by plants ands animals.
Some common experiences of new fish keepers include problems associated with this Nitrogen Pathway. 
Commonly referred to as the ‘Nitrogen Cycle’, the Nitrogen pathway is really not a cycle, but a line.  The fish produce ammonia, Nitrosomas convert it into Nitrite.  Nitrobacter converts the Nitrite into Nitrate and we end up with Nitrate.  The fish don’t utilize nitrate, so it’s not a true cycle.
In a new tank we are lacking established populations of Nitrobacter and Nitrosomas bacteria.  We put in our new fish and they produce ammonia.  But instead of the conversion to nitrite, it sits.  And kills the fish.  In many new tanks, you will see a white haze in the tank.  This is accumulated ammonia in solution.  It has yet to be removed/converted by bacteria.  Because our new tank is sterile, it does not have any living bacteria to help with this.  We solve this problem in three ways.  1) Do nothing.  Not the best as it puts those first few hardy fish under tremendous stress of high ammonia, and then high nitrite levels.  All fish carry these same bacteria in their intestines and mouths, so some will eventually fined there way to the filter and grow.  But you can have deadly spikes in ammonia and nitrite and heavy fish loss. 2) Supplement with a commercial bacterial product.  I like to do this.  There has yet to be a miracle product that does it all, so don’t believe the ads.  But it does make it less rough on the fish and helps speed things up  bit.  All told, it takes about 21 to 28 days for this to occur.  A bit less with  a bacterial supplement.  3) Is to introduced a seeded filter bed.  This is ideal, as you have a working filter material with millions of  living bacteria. This is the best method as it reduces the wait to just a few hours.  Its a shame more pet stores don’t offer this as a service to the customers, as it would allow many more fish success and bring back return customers again and again.
High Ammonia
If you have a high level of ammonia in your tank it is a sign of 1) a new tank, 2 overfeeding, 3) recent use of medication 4) filter malfunction 5) overcrowding.  Some of these problems can be prevented, others can be eliminated altogether.
If you have  a high ammonia level, you need to do a partial water change right now!  Do a 50% now.  If your ammonia is 4.0 PPM and you change 50% of the water, you will end up with a 2.0 PPM, still deadly on the scale.   But you don’t want to risk shocking the fish with temperature of pH, etc. too much, so start with a 50% water change.
Next, evaluate your pH.  Actions or circumstances that cause a decrease in pH cause Many times a rise in ammonia.  If it’s 6.5 to 7.0 just monitor it.  It’s not too low to be a problem to any fish except marine fish and some African cichlids.  If its above 7.0 we have to be even more concerned  Ammonia become ammonium (NH4+) at pH over 7.0  And Ammonium is even more toxic than ammonia (NH4).  If the pH is above 7.0 then you should try to adjust it slowly back to 7.0 with the 50% water change you are working on.
Next we have to evaluate why the high ammonia exists.  Is it a new tank?  If so, then you have a problem with ‘New Tank Syndrome”.  This is because a new tank is relatively sterile and does not yet contain the beneficial bacteria to breakdown fish wastes and convert them to less toxic materials.  If this is the case, you need to hold off on any new fish and see if you cab help the process along with a commercial supplement or a seeded filter.
Is the tan overcrowded?  How do tell if the tank is overcrowded?  Well, typically, you can assume 1 gallon of water per inch on fish in any direction.  That means a Neon Tetra needs on gallon.  A 3-inch Angelfish needs 3 gallons for its length, plus another 3 for its height., for a total of 6 gallons.  This is a rule, and there are always exceptions.  One noteworthy exception is the goldfish.  They are exceptionally messy fish.  They like even more space, along the lines of 5 gallons per inch.  That means that cute 1-inch goldfish needs a 10-gallon filtered aquarium gallon to thrive!  If you determine the tank is overcrowded you have  a few options. You can see if your local fish store will  take back a few of the extras, or see if another fish keeper will take them for you, or you can get a larger tank.  It’s a common mistake that adding another filter to a smaller tank will help.  For a quick and temporary fix, it will,.  But fish need space too, and this does not provide them the space they need.
The increase in ammonia may also be from recent use of medication. Most medications are antibiotics, designed to kill bacteria that infect out fishes. The beneficial bacteria that breakdown the ammonia are also a type of bacteria.  Many of the medications used to treat fish will actually harm the ‘good guys’ as well.  This is why it’s best to treat fish in a separate tank.  If you have recently treated the tank, then you consider the problem to be the same as if you had a brand new tank. 
Filter malfunction can also cause a rise in ammonia.  If the filter stops filtering because of mechanical malfunction, then the water builds up the ammonia.  Regular inspection of the intakes, hoses, motors and impellers if your filter has one is recommend to prevent this from occurring to you.  The other possible problem with filters is clogging.  All filters have some sort of insert for mechanical filtration.  Many items this is a sleeve or sponge of foam of floss.  This needs to be rinsed and checked about once per week to keep it clean and free from debris.  If  it’s less than 3 weeks old and it brown and smelly, then you have a classic case of overfeeding.
And overfeeding is the next cause of an increase of ammonia.  If you feed your fish too much, the excess wastes become ammonia because of the normal fish metabolism.  Think about it.  Fish in a tank have a simple existence.  The temperature is controlled, there are no predators to run from (we hope you have selected compatible fish) and all food is provided.  So there energy requirements are less than that of the fish migrating up river.  It is best to feed our aquarium pets a few SMALL meals daily.  That means just a few flakes or pets two to three times a day.  Don’t worry if everyone doesn’t get some.  The ones who miss a meal in the morning will be first in line for the evening meal!
So now you know why you have an increase and you have performed that first 50% water change.  You now have stop feeding for 24 hours and re-test.  In 24 hours do another 50% water change and re-test.  You should notice an improvement.
FILTRATION TYPES
Why you need Filtration
Sometimes we forget that fish kept in an aquarium are confined to a very small quantity of water as compared to their natural habitats in
the wild. In the wild, fish wastes are instantly diluted. But in an
aquarium, waste products can quickly build up to toxic levels.
These waste products include ammonia released from your fishes’ gills,
fish poop, and scraps of uneaten food. The food and the poop will also
eventually decay, releasing ammonia. Even small amounts of ammonia
will kill your fish.
Obviously, the more sources of fish waste, the quicker and greater the
ammonia problem. A small heavily fed tank with lots of large fish will
have much more ammonia than a large tank with one seldom-fed small
fish. But for both these cases you need some form of aquarium
filtration to control the toxic ammonia.
Some aquarists try to control ammonia levels exclusively by changing
the water. This is helpful, but impractical because of the frequency
and size of the water changes required.
  
Fortunately, there is an easier way! In fact, the world is full of
bacteria that want nothing more than to consume the ammonia and
convert it into less toxic substances. For many an aquarist, this
process occurs without their knowledge or help. However, the smart
aquarist will learn how to take advantage of this beneficial bacteria
by maximizing its growth.
  
When you start a new fish tank, colonies of beneficial bacteria have
not yet had the chance to grow. For a period of several weeks this is
hazardous to fish. You must gradually build up the source of ammonia
(i.e., start with only one or two small fish) to allow time for the
beneficial bacteria to grow. This is called “cycling” your tank.
  
Remember that the bacteria break down the ammonia into substances
 (first nitrate, then eventually nitrate) that are merely less toxic,
rather than non-toxic. Many fish can tolerate reasonably high levels
of nitrates, but over time the nitrates will accumulate until they,
too, become toxic. Also, because nitrate is a fertilizer, high nitrate
levels can lead to excess algae growth.
  
WATER CHANGES
Although there are many ways to remove excess nitrate, the most
effective way is to regularly change part of the water. This is one of
the most neglected and important parts of aquarium maintenance!
How often and how much you need to change depends a lot on the waste
load in your tank, and the sensitivity of your fish. You don’t want to change ALL of the water at any point in time because the change in water chemistry will be stressful to your fish. The best way to decide how often and how much to change your water is to monitor your water quality with water tests. As a minimum, if your tank is new, you should test for ammonia and perhaps nitrite. In established tanks you should monitor for nitrate accumulation. Water tests are the most reliable way to know how well your aquarium filtration works.
For an average tank, you should change no more than one third of the water in 24 hours. Many aquarists with average aquariums change a quarter of the water every two weeks. Your aquarium is probably not average, and you really should measure nitrate levels to determine your water change schedule.
  
  BIOLOGICAL FILTRATION
 
   Biological filtration is the term for fostering ammonia neutralizing
   bacteria growth. It is so important to the health of your aquarium
   that we should look at how this process works more closely. (There are
   other types of wastes that can cause problems, but the regular partial
   water changes needed to control nitrates are typically enough to
   control other forms of waste as well.)
  
   Mother Nature provides several types of bacteria that break down
   ammonia into progressively less toxic compounds. First, nitrosomonas
   breaks ammonia into nitrites. Then nitrobacter breaks the nitrite into
   nitrate. These bacteria are not harmful and are quite abundant in
   nature. They are so common that we do not need to add them to our
   aquariums; nature does it for us.
  
   In the presence of ammonia and oxygen these bacteria will naturally
   multiply. The bacteria attach to the tank, rocks, gravel, and even
   tank decorations. Note that we have not yet said anything about a
   physical filter. This is because biofiltration bacteria require only
    1. A surface upon which to attach,
    2. ammonia for food, and
    3. oxygen-rich water.
      
   This sounds so simple; why do we need a physical filter?
  
   Actually, if you limit the amount of fish to what the natural
   biofiltration can handle, you do not need a physical filter.
   Unfortunately, you cannot support very many fish with only the natural
   biofiltration.
  
   In the last few decades, the hobby has seen many new types of
   biological filters invented which can vastly increase the capacity of
   the bacteria colony to provide biological filtration to your aquarium.
   In essence, all of these types of filters provide additional surface
   area for bacteria attachment and increase the available oxygen
   dissolved in the water.
  
  MECHANICAL FILTRATION
 
   Remember that ammonia comes directly from the gills of your fish, but
   also from decaying fish poop and food scraps. If you can mechanically
   filter out the poop and the waste food before it gets a chance to
   decay, you can be a step ahead in the game. Not to mention that these
   wastes are ugly and can detract from the beauty and enjoyment of your
   aquarium.
  
   Simply stated, mechanical filtration is the straining of solid
   particles from the aquarium water. Mechanical filtration does not
   directly remove dissolved ammonia. Most common mechanical filter media
   do not remove microscopic bacteria and algae from the water. Neither
   will mechanical filtration remove any solids trapped by gravel,
   plants, or decorations.
  
   You will need another method to remove the solid wastes from the nooks
   and crannies of your aquarium. One of the easiest methods is to
   “vacuum” the gravel, etc., as part of your regular water change
   routine and everybody should do this. (Note that those marine
   aquariums, which use live substrates, are an exception.) Some people
   install circulation pumps, known as wave makers, to improve the chance
   of catching solid wastes in the mechanical filter.
  
   The four most popular mechanical filtration media are sponges, paper
   cartridges, loose and bonded floss media, which are reusable to
   different degrees. Clean paper cartridges have the smallest openings
   and clean bonded floss has the largest openings. Clean sponges and
   clean loose floss falls somewhere between.
  
   A filter media with small openings catches finer particles, but clogs
   faster. Also, as a rule, a physically large filter area will clog more
   slowly than a small filter. As the filter media gets dirty it will
   trap smaller and smaller particles. At some point the media is so
   clogged that it will not pass water.
  
   SUMMARY: A good mechanical filter is one that traps enough solids to
   keep the water clear without plugging too often.
  
  CHEMICAL FILTRATION
 
   Chemical filtration, in short, is the removal of dissolved wastes from
   aquarium water. Dissolved wastes exist in the water at a molecular
   level, and fall into two general categories, polar and nonpolar. The
   most common chemical filtration method involves filtering the water
   through gas activated carbon which works best on the nonpolar wastes
   (but also removes polar wastes). Another effective method is protein
   skimming, which removes polar wastes such as dissolved organics.
  
   Gas activated carbon (GAC) is manufactured from carbon, typically
   coal, heated in the presence of steam at very high heat. This process
   causes the carbon to develop huge numbers of tiny pores, which trap
   nonpolar wastes at the molecular levels by means of adsorption and ion
   exchange, and removes heavy metals and organic molecules, which are
   the source of undesirable colors and odors, through a process known as
   molecular sieving. Be sure that when you place GAC in your filter,
   that the filter water flows “through” the GAC granules and not
   “around” the GAC.
  
   Most GAC, which is marketed to the aquarium market, is intended for use
   in filtering aquarium water, except coconut shell GAC which is
   intended for use in the removal of wastes (such as odors) from air.
  
   In reef aquariums, some people are concerned about phosphate leaching
   from low quality carbons, though there are mixed opinions on the
   problem. As a rule, buy only carbons made by reputable aquarium supply
   companies, and if in doubt, test the GAC for phosphate before use. GAC
   cannot be rejuvenated.
  
   In freshwater-planted aquaria, some people are concerned about GAC
   removing trace elements required by plants for healthy growth.
  
   A variety of special chemical filtration media have been developed to
   remove specific chemicals. A common one is made from the zeolite clay
   (also used as some cat litters), and is marketed under such brand
   names as “Ammo-Carb”. This media removes ammonia from water, and is
   good for short term use. The aquarist should be aware that if zeolite
   is used, especially when cycling a new aquarium, then the
   establishment of natural biological filtration will be delayed or
   disrupted.
  
   Protein skimmers are primarily used in saltwater aquaria, especially
   reefs. They have the remarkable ability to remove dissolved organic
   wastes before they decompose. The process involves taking advantage of
   the polar nature of the organic molecules, which are attracted to the
   surface of air bubbles injected into a column of water. The resultant
   foam is skimmed off and discarded.
  
FILTER TYPES
  THE CORNER FILTER
 
   For decades, hobbyists have successfully kept fish healthy and happy
   through the use of the $2.49 corner filter. Typically, they are clear
   plastic boxes, which sit inside the tank. An air stone bubbles air
   through an air lift tube, which forces water through a bed of filter
   floss or other media. mechanically filtering the water. Colonies of
   bacteria build up on the media, providing excellent biological
   filtration. (It is important to change only some of the media at any
   given time! This way the bacteria does not get wiped out.) Nowadays
   people don’t use corner filters as much because they’re ugly, take up
   space in the tank, and require a bit more frequent maintenance than
   other filters. But you can’t beat the price.
  
   Another use of the corner filter, that is not really matched by other
   filter types, is as an impromptu quarantine tank filter. If you have
   the need to set up a second tank on the quick, you can take some
   gravel from an established tank and put it in a corner filter, and
   immediately, you will have a functioning biological filter. This way
   you can turn a five gallon bucket into a quick and cheap
   hospital/quarantine tank on a moment’s notice.
  
  UNDERGRAVEL FILTERS
 
   Fish stores commonly sell undergravel filters (UGF’s) to beginners in
   “aquarium kits” because they are cheap, and they work (for a while).
   They work by slowly passing water through the bottom gravel, which
   sits on top of a perforated plate. The water can be pumped with an air
   lift, with bubbles air lifting the water in a vertical tube attached
   to the filter plate. Also, some people prefer the increased water flow
   achieved with submersible pumps, called powerheads, attached to the
   same lift tubes.
  
   UGF’s make good biological filters, because the slow flow of water
   through the gravel fosters large colonies of beneficial bacteria which
   neutralize toxic ammonia. The hitch is, that UGF’s are awful
   mechanical filters. Fish waste gets pulled out of sight into the
   gravel. Before you know it, the gravel clogs up. You then have a big
   mess and a health risk to your fish!
  
   A partial solution to this dilemma is to run the powerhead in reverse,
   sending water up through the gravel. This technique is known as
   Reverse-flow Undergravel Filtration (RUGF); conversion kits or
   special powerheads can be purchased to accomplish this. The intake of
   the powerhead is covered with a porous sponge which serves to
   “prefilter” out some of the waste that can clog the gravel. In
   actually practice, this helps, but is only a partial solution.
  
   If you choose to use an UGF/RUGF, you must regularly vacuum your
   gravel. Fish stores sell siphon hoses with a “wide mouth gravel
   vacuum tube” attachment that “washes” the gravel during your
   regular water changes. IF you clean your gravel regularly, and
   maintain a regular and frequent partial water routine, UGF’s and
   RUGF’s are an economical and effective aquarium filter in freshwater
   aquariums, and in lightly stocked saltwater fish-only aquariums.
  
  SPONGE FILTERS
 
   Sponge filters provide an efficient and cheap form of biological
   filtration. Water is forced through a porous foam, either by a
   powerhead, or air bubbling through an airlift tube. Water flowing
   though the sponge allows the growth of a colony of beneficial bacteria
   which neutralizes toxic ammonia.
  
   One style of sponge filter uses two sponges attached to one lift tube.
   These have the advantage that the sponges can be cleaned one at a
   time, reducing bacterial loss. Also, one of the sponges can be removed
   and transferred to a new tank, bringing with it a colony of beneficial
   bacteria, and thereby “jump starting” the cycling of a new tank. Some
   enlightened fish stores sell these double sponge filters to beginner
   customers when they sell a tank kit. They take one of the new sponges
   out of the “box” and swap it for a old established sponge in one of
   their tanks in their store which is carried home in a plastic bag.
  
  POWER FILTERS
 
   Most people agree that power filters are much easier to maintain and
   can be as economical as undergravel filters. There are many styles of
   power filters, but the most common hangs on the back of the tank. A
   siphon tube pulls water from the tank into the filter box and passes
   the water though a mechanical filter (typically a porous foam sponge).
   The sponge doubles as a biological filter. A internal pump then
   returns the filtered water into the aquarium. These power filters come
   in many sizes suited for small to large aquariums.
  
   The foam sponge can be easily inspected for clogging or removed for
   cleaning. You must clean the sponge regularly to remove the solid
   wastes before they decompose and dissolve back into the water. It is
   quite important that when you clean the porous foam that you do not
   kill the bacteria colony through the use of detergents, very hot or
   very cold water. A safe and easy way is to rinse the foam sponge in
   the bucket into which you have just drained some tank water during
   your regular water change routine.
  
   Power filters now come with all sorts of fancy “features”. Most
   allow placement of a chemical filtering media, typically granular
   activated carbon, in the water path.
  
   Another development in the last few years is the “wet-dry wheel”
   (called a biowheel by one manufacturer). The beneficial bacterial
   colonies that neutralize toxic ammonia require an oxygen rich
   environment to grow. The “wet-dry wheel” passes water over a water
   wheel device which sits outside (on the edge) of the aquarium. This
   rotating wheel maximizes available oxygen allowing a large bacteria
   colony to flourish. One drawback is that these wheels have been known
   to jam, so you need to check them frequently. Other than this minor
   point, the “wet-dry wheel” is an excellent method of providing
   vigorous biological filtration.
  
  THE CANISTER FILTER
 
   Canister filters have some similarities with the “hang on tank”
   style of power filters, but the essential difference is that canister
   filters are designed to provide more powerful mechanical filtration.
   Typically, the water is pumped, at moderate pressure through a filter
   material, such as glass wool, or a micron filter cartridge. Canister
   filters are especially useful in aquaria with large or numerous messy
   eaters that generate a lot of waste. For these filters to be effective
   they must be frequently cleaned, to avoid the decomposition of waste
   in the water stream.
  
   These filters usually sit on the floor below the tank, but also can
   hang on the tank, and in some designs even sit inside the tank, in
   which case they are called a “submersible filter”. Some hobbyists
   attach a “wet-dry wheel” to the outflow of their canister to improve
   the biological filtration capacity of this type of filtration system.
  
  WET/DRY FILTERS
 
   Also known as trickle filters, wet/dry filters work on the principle
   that the beneficial colonies of ammonia neutralizing bacteria grow
   best in the presence of well oxygenated water. By “trickling” water
   over unsubmerged plastic gizmos or other media, wet/dry filters
   provide a very large air/water surface area. They come in many shapes
   and sizes. The boom in successful saltwater aquariums in the 1980’s
   can be attributed to the use of this filter type.
  
   Many things can used for the media, with the best providing great
   amounts of surface area, while at the same time having large openings
   to reduce the tendency to clog and ensure efficient gas exchange. The
   problem of clogging of the media can also be reduced by prefiltering
   the water with an efficient mechanical filter, and (when used) with a
   protein skimmer.
  
  PROTEIN SKIMMERS (AKA FOAM FRACTIONATORS)
 
   Protein skimmers were initially developed for use in industrial sewage
   treatment plants where they are also known by the term foam
   fractionator. Protein skimmers have the unique ability to remove
   dissolved organic wastes BEFORE they decompose! This is a neat trick
   which is accomplished by taking advantage of the fact that organic
   chemicals are attracted to the surfaces of bubbles, which are passed in
   large numbers through a column of water. The foam is then “skimmed”
   off the water, while at the same time removing the organic wastes. The
   foaming process only works in a water with high pH and salinity, and
   as a result skimmers are primarily for saltwater use.
  
   The protein skimmer is largely responsible for the boom in reef
   aquaria in the 1990’s, due to the high water quality possible with
   this type of filtration. A current “state of the art” in reef
   systems is based upon the use of protein skimmers and live rock
   without the use of a wet/dry filter. This school of thought is known
   as the “Berlin method”.
  
  FLUIDIZED BED FILTERS
 
   Very recently, some hobbyists have reported success with a new type of
   filter which uses a fluidized bed of sand. This filter is roughly
   similar in principle to the reverse flow undergravel filter, but with
   much higher water flow. The higher water flow keeps the sand clean of
   debris, while at the same time allowing the development of large and
   efficient colonies of beneficial bacteria. Reported problems include
   oxygen depletion and clogging.
  
  DENITRATORS
 
   Another specialized type of filter is designed to help in the control
   of the accumulation of nitrates, the end product of the neutralization
   of ammonia by the biological activity of bacteria. These fall into two
   categories, the anoxic bacterial, and the plant/algal scrubbers
   (discussed in the next section). It has been discovered that colonies
   of bacteria which grow in oxygen poor environments can be harnessed to
   biologically consume nitrate, and release harmless nitrogen gas. This
   method is achieved in one of two ways. The process was first developed
   in the 1980’s through the use of a box system, coil, or porous foam
   block which allowed very slow transmission of nitrate-laden water.
   Inside the box/coil/foam, sugar was placed, and the slow passage of
   water quickly became anoxic. In these anoxic conditions, bacteria
   would grow and consume excess nitrate. Many aquarists have reported
   failure in their attempts at this type of filtration.
  
   More recently, hobbyists have developed similar anoxic conditions
   below plates at the bottom of their tanks buried in fine sand. In the
   saltwater systems, these sand beds are referred to as “live sand”. In
   freshwater planted systems, fine grain substrates are allowed to
   develop anoxic zones which probably also have a denitrification
   capability.
  
   The Berlin Method of reef aquariums involves the use of large
   quantities of live rock harvested from tropical reefs. Aquarists
   report good nitrate control in live rock systems, which, though not
   well understood, probably involves the denitrification of the nitrates
   within the interior of the rocks. Another school of thought is that
   the heavy growths of calcareous algae on the live rocks in Berlin
   Method reef aquariums consume nitrate.
  
  ALGAL SCRUBBERS
 
   Algal scrubbers use live algae to do the “filtration”. Water is run
   over a wire mesh in a trough under bright lights, where algae is
   encouraged to grow. The growth of the algae removes some pollutants
   from the water. This is a controversial form of filtration for reefs
   and large marine ecosystems invented by Dr. Adey at the Smithsonian.
   Some believe it is a complete filtration solution, others claim its
   use leads to poor water quality and algae growth in the tank as well.
   In freshwater-planted aquariums vigorous plant growth has been
   observed to beneficially consume excess dissolved nitrates.
  
  CHILLERS
 
While not really a filtration, saltwater aquarists occasionally have the need to lower the temperature of their aquarium water. The high light levels needed in reef aquaria involve a build up of excess heat. Use of a hood fan and removal of the ballast from the vicinity of the tank can also help. Submerged pumps are also a source of unwanted heat, and as a solution, reef aquarists favor the “non-submerged” pumps due to the decreased transfer of heat to the water.
  
 A little recognized source of heat control is through the natural cooling effect of evaporation in wet dry filters, and through the flow of air over the surface of the aquarium. Nevertheless, additional
 cooling is often required, especially in warm climates.
  
 This is achieved through the use of “freon” style cooler units similar to home refrigerators. They either pass the water through a heat  exchange unit, or pass coolant through a heat exchanger in the tank. Those chillers are expensive but not many people have had success in the “do it yourself” construction of chillers. (The “dorm” type of refrigerator is not powerful enough to be of use, just in case you were thinking about this.)
Aquarium Maintenance
When set up properly, marine aquariums require minimum maintenance. The operative word is properly. However, regular preventive checks of equipment are needed to ensure proper functioning of the entire aquatic system. Weekly and monthly maintenance tasks are required. In addition, a series of daily checks should be made. especially during the first few weeks after the first aquatic animals have been added. Routine daily inspection of the aquarium system ensures that problems can be found quickly and corrected before they place the fish and invertebrates in jeopardy.
As a safety procedure, whenever working with aquarium equipment make sure that the apparatus is disconnected from electric outlets. Always plus appliances into a Ground Fault Interrupt Circuit and make sure to use drip loops in all cords. Saltwater is highly conductive and can transmit dangerous electric shocks. This is especially true when working on lighting elements or adding water to the aquarium .
It is also important to make sure that your hands are free of detergents or any other substance  that could be toxic to the fish and invertebrates. If you need to remove an item from the aquarium, first wash your hands and arms well with plain warm water. Any products you use to clean the aquarium must also be free of detergent residues or other possibly toxic materials. It is recommended that you purchase brushes. sponges, buckets, and other items that will be used only in the maintenance of your aquarium.
Daily Maintenance
Each day a series of checks should be made to ensure that everything in the aquarium is functioning properly. Besides turning on the aquarium light and feeding your fish, you should also routinely remove any food materials or other debris is visible on the substrate. You should also fish and invertebrates and observe and behavior.
Filters, Heaters, and other Equipment
The next daily check involves the functioning of the filters, lighting, heaters, air stones, protein skimmers, and other apparatus. The undergravel filter should be examined to ensure that the proper amount of air is flowing to operate the lift tubes. If the airflow appears diminished, it could be caused by a faulty air pump, clogging of the airline by accumulation of salts, or clogging of the air diffuser in the undergravel lift tube. Salt accumulation is not unusual in aquariums that have been in operation for several months or more. The salt can be removed by passing a fine wire down the plastic air tube in the filter to break up the salt accumulation. If this is not effective, it may be necessary to detach the filter tube assembly from the undergravel filter and soak the parts in warm water to dissolve the salt deposits.
Other filters, including an outside filter or canister filter, should be examined to ensure that they are operating properly. [f you notice a diminished water flow, this indicates that the filter medium has become clogged with particulate matter and debris and requires servicing. Diminished flow could also be caused by a crimp in the hoses of the filter.
The light bulbs should be inspected for any signs of malfunction and replaced if necessary.
The aquarium heater should then be checked to make sure it is operating properly and the aquarium water temperature is within the acceptable range. A properly functioning heater keeps water temperature within the set range. A slight fluctuation is acceptable and will not harm the inhabit-ants. If the aquarium water is cooler than desired, adjust the heater control knob or dial accordingly. Do this gradually, following the instructions provided by the manufacturer of the heater. A safe approach is to turn the heater dial until the thermostat light just comes on. Then wait several hours, check the temperature and read just as required.
If your aquarium is equipped with a protein skimmer, check to see if it is operating properly.   If necessary, adjust the airflow to the skimmer, empty the organic and waste that has accumulated in the collecting cup.
Finally, check to make sure that the air stones are operating properly. As with undergravel filters, air stones can become clogged over time as they accumulate dirt and salt. If a decreased airflow is noticed it may be necessary to remove the air stone and to clean it well in fresh water. A decrease in airflow can be caused by crimped airline tubing, improperly adjusted air valves, faulty air pump, or salt accumulation.
The condition and quality of the water should also be examined daily. In a properly maintained aquarium, the water should  be crystal clear and should smell fresh. Questionable odors could indicate the need for a water change. Water deterioration could be due to improper filtration, decaying food, or a dead fish or invertebrate.
Fish and Invertebrates
Daily inspection of the fish and invertebrates in your aquarium ensures that they are accounted for and in good health. This is best done during feeding when the majority of the fish swim in the open. If a certain fish is not readily seen, do not assume that it has died. Since the behaviors of  fish differ, some may readily come into the open.
For example, squirrelfish tend to hide during the day and feed during the night, while many species of wrasses hide in the sand for long periods of time. However most healthy fishes, including squirrels, soon adapt to the feeding schedule, whatever it may If a particular fish is not seen for several days, examine the aquarium closely, as it may have died. It is also possible that it jumped out of the tank if there was an opening in the aquarium cover . This is not uncommon, especially with certain species like jawfish. First, look on the floor around the aquarium. If the fish is not found. it will be necessary to •'” move the rocks a decorations in the aquarium to locate the fish. This should be done carefully and with as little disturbance as possible to the other fish and invertebrates.
                               
In addition to checking for the presence of aquarium inhabitants, their general condition should be noted each day.  The fish should be examined to see if they are behaving normally.  Abnormal signs such as increase in respiration, scratching along aquarium surface, or frayed fins can indicate deterioration of water quality, aggression by other tank mates, or the onset of disease.
All living corals should be examined. If any invertebrates have died, remove them promptly and follow up with an ammonia test. An ammonia test is especially important if the aquarium water is cloudy or has a peculiar odor.
Water Testing
Besides a general observation of water clarity, water tests including pH, ammonia. salinity, or any other tests should be performed as required for routine weekly maintenance. Water tests need not be performed daily except during the initial establishment of the biological filter or when new fish are added to the aquarium.
Weekly and Monthly Maintenance
Water Changes
Regular water changes are fundamentally important in any aquarium. Even though aquarium water is filtered to remove toxic components, various organic and inorganic compounds accumulate in the water over time. In fact, if an aquarium is left without any water changes, radical alterations in the chemical composition will adversely effect the aquarium inhabitants. These alterations include an increase in nitrate, decrease in pH, decrease in the buffering capacity, increase in the concentration of phosphate, increase in organic compounds, and reduction in various trace elements required by marine organisms, especially invertebrates.
Ok, so you have a new (or old) fish tank.  You know you need to clean it, but how.  Do you tear down the whole tank and start from scratch?  No way!  Not only is it too much work, but its too much stress for the fish and bad for the overall system.  So what should you do?  Partial water changes.
The partial water change is just that, a partial removal of a volume of water from the tank and replacing the water with fresh water.  This is beneficial because it will replenish many minerals and vitamins that become soluble in water.  Remove many dissolved organics from decorations like driftwood, and it removes accumulated nitrogenous wastes like nitrate.  It is also beneficial in aiding the buffer of the tank pH. 
How much water makes a partial water change?  A few different schools of though come into play here.  Both systems work.  Choose the one that will be most likely for you to adhere to.  I like to do smaller, weekly water changes.  In small tanks (less than 55 gallons) I do a 5 to 7% water change each week.  In bucket speak, this roughly equals 2 to 4 buckets of water.  In a larger tank, I do 10% weekly.  A more relaxed method is to do 20 to 25% monthly water changes.  This had the added advantage of not taking an hour of your free time every week.  Both of these will do the job.  Of course, smaller frequent water changes are more gradual and will keep all dissolved organic levels lower, but the key is to actually do the work.  So pick the plan that you can live with.  Certain fish will dictate their own water change plan.  Some fish, like Discus like more frequent water changes, and some marine tanks, reef systems in particular may require more frequent water changes. 
When doing your weekly or monthly water changes, it is important to also do some tank maintenance.  Use a gravel vacuum and stir up that gravel.  This is the most important part of doing water changes.  By siphoning the gravel, you remove all the accumulated detritus from the gravel.  All the fish wastes, and uneaten food that has accumulated there over the past days.  If you have an undergravel filter, this also helps stir up the filter bed and eliminate any dead spots that may form.  A dead spot is any region  where the water flow becomes blocked or stagnant.  You may notice a rotten egg smell when doing your water changes if you stir up any dead spots.
Along with vacuuming the gravel, you need to treat the water.  If you have municipal, or city water they often treat it with chlorine or chloramine to help keep it clean.  Both chlorine, the same stuff you use in pools, and chloramine is chlorine with ammonia added.  Both are highly toxic to fish, and need to be removed.  There are literally dozens of products out there for this purpose.  Some remove chlorine only, other both.  Some add ‘slime’ to the fish, others add electrolytes, etc.  Make sure you use one that I suited for your water conditions.  And if you have a well, you do not have to de chlorinate the water.  Mother Earth does not yet self chlorinate.  But you will have to check for hardness and pH.  Many times well water is very hard.   Meaning it has a lot of dissolved minerals like calcium and magnesium in it.  This is fine for some fish, but not so for others.  So you should treat the water to adjust hardness and pH to a level that resembles your tank.
And while you are adjusting and treating your water, adjust that temperature.  No one likes to have their hot shower interrupted by blast of cold water.  Well, no fish like to have a sudden drop (or increase) of 10 degrees in the tank!  This kind of stress is easily avoidable and will save you countless hours of grief.  Temperature shock is a leading cause of parasitic infection.
Increase in Nitrate:
We previously noted that once an aquarium biological filter is functioning there will be a continuous accumulation of nitrate. Even though it has generally been accepted that nitrate is not toxic, recent research suggests that high nitrate levels can interfere with the normal growth of marine fishes and have an effect on the longevity of invertebrates.
Decrease in pH:
Although several factors affect the decline of pH in aquarium water, chemical by-products of nitrification are particularly noteworthy. As previously mentioned (see page 85), the nitrification process results in an accumulation of nitrite and nitrate. However, these compounds are initially added in the form of nitrous acid and nitric acid, which eventually become nitrites and nitrates through neutralization by natural buffers. As the buffer capacity of the water is reduced, an accumulation of acids lowers the pH.
Decrease in Buffering Capacity:
Natural seawater has compounds that buffer the water and maintain n the appropriate ate alkalinity. Over time, the buffering capacity of the water lessens. The buffering compounds in the substrate eventually also become exhausted. Since synthetic sea salts contain buffers, the regular replacement of water restores any diminished buffer capacity.
Increase in Phosphate:
 The buildup of phosphate in aquarium water also upsets the chemical balance. Phosphates originate from the breakdown of various organic materials and accumulate regularly. Although phosphate is not toxic at concentrations normally found in aquariums, high concentrations will coat substrate particles and prevent the release of buffering chemicals. Partial water changes greatly aid in reducing phosphate.
Increase in Organics
An increase in organics is another problem in marine aquariums. As discussed in The Aquarium Conditioning Period various filter media as well as protein skimmers will remove organics. Partial water changes also reduce the concentration of organics and the accompanying yellow color of the water. High concentrations are known to inhibit the normal growth of fish and invertebrates.
Reduction in Trace Elements:
Trace elements are found in all synthetic sea salts and in natural seawater. Many trace elements are required by various marine animals for specific biological functions. For example, iodine is found in very small concentrations in seawater, but it is necessary to prevent goiter in fish. Various invertebrates accumulate large concentrations of certain trace elements, although their function is not clearly understood. The growth of macroalgae can also rapidly deplete certain trace elements. Regular water changes help restore the trace element balance in aquariums.
As can be seen, regular partial water replacement therefore provides the numerous benefits of restoring and maintaining proper water quality.
Partial water changes of 25% or more should be accomplished monthly, or better yet, a 5 to 10% weekly water change should be done. The recommended procedure is first to mix sea salt with the appropriate amount of replacement water the night before the water change and adjust the salinity to that of the aquarium. The next day, using a siphon, remove an equivalent amount of water from the aquarium and replace with the newly mixed seawater.
Replacing Evaporated Water
It is important to replace evaporated water weekly to maintain the proper salinity and chemical balance. Tap water can be used, but in with extremely hard water, the continual addition of tap water can eventually cause a chemical imbalance. Under such circumstances distill water should be used alternately with tap water to minimize the possibility of chemical alteration of the aquarium water. It must be remembered that to destroy any chlorine or chloramines. municipal water needs to be treated with a water conditioners prior to addition to the aquarium.
Cleaning Aquarium Surfaces and Equipment
At least once weekly, all aquarium equipment should be wiped with a clean cloth. This should be done especially on areas where salt has accumulated, including the aquarium cover, hood, top, and sides of the aquarium. With removable aquarium covers, the easiest way to clean off collected I salt and dust is to remove the cover and scrub it under warm running water.
The outside and inside glass should also be I cleaned. The outside of the aquarium can be wiped with a cloth and a little glass cleaner. Be careful to use only a small amount of the cleaner • and never use it on the top of the tank where it could get into the water.
The inside glass can be cleaned using various manufactured devices for removing a buildup of algae. One popular device is the cleaning magnet.
Two magnets are equipped with special non-abrasive cleaning surfaces. One magnet is placed   inside the aquarium and another on the outside.
The magnetic force holds them in place. You simply move the outside magnet that moves the inside, magnet to remove attached algae. If the inside magnet accidentally detaches during cleaning, remove the inside magnet, rinse the cleaning surface I and inspect for any small stones. If this is not done, remaining sand or gravel will scratch the inside surface of the aquarium. This is especially important when cleaning acrylic tank surfaces, which damage easily.
Aquarium glass can also be cleaned with algae scrapers or cleaning sponges. This device uses razorblades attached to a long handle. The movement of the cleaning head scrapes algae off the glass. The sponge type has a sponge attached to a long handle that will also remove algae from the glass. As with the cleaning magnets, you will avoid damage to the aquarium by frequently inspecting the cleaning head of either device to make sure small particles or stones are not trapped.
Replacing Fluorescent Bulbs
The fluorescent bulbs used in the aquarium hood have a finite life and must be replaced periodically. The bulb may still be functioning, but the intensity of the light will gradually diminish.
Check with the manufacturer to find out how often to replace the bulbs. For example if a bulb is rated for a 5,000-hour life and your aquarium is illuminated for 10 hours daily, you will need to replace the bulbs approximately every 7 months.
Cleaning Decorative Aquarium Items
Generally, there is little or no need to clean the various decorative items used in the marine aquarium. Algae will grow on various rocks, coral, and shells, in time giving the aquarium a more natural appearance. In addition, small invertebrates will colonizing these areas. From time to time, however. you may wish to clean off excessive growths of algae or accumulated dirt and sediment from coral and shells. These items can be removed, cleaned, and rinsed with a small clean toothbrush in fresh water. Never use any type of cleaning solvent or detergent to clean decorative   items. These products are toxic to fish and invertebrates. Decorative items generally need to be cleaned only once every 3 to 4 months or more.
Cleaning Aquarium Filters
The various types of filters used in marine aquariums require maintenance to ensure performance. Depending on the filter type, maintenance needs to be done anywhere from every 3 to 12 weeks. You should follow the manufacturer’s instructions  for cleaning of filters and replacement of media.
Undergravel Filters: Since these filters utilize the aquarium gravel as their filter medium, the layers of the filter bed can become laden with debris. If the filter bed becomes clogged, the filter will not function properly. Therefore. it is important to gradually stir up the top layer of the filter bed once every few weeks to dislodge particles and ensure a uniform flow of water through the filter bed. The debris that is stirred up will be removed by an outside filter bed.
If the undergravel filter bed is heavily laden with organic materials, use a special siphon cleaner that removes water as it cleans the lop surface of the filter bed. This process can be followed once every 4 to 6 weeks or as required. The frequency is lessened when the aquarium is equipped with an additional outside filter.
Outside Filters, including canister filters, re-quire cleaning every 4 to 8 “weeks. depending on the biological load in your aquarium. This entails removal and replacement of the’ activated carbon and filter floss. Always retain a portion of the old floss and add to the new floss. This ensures that some of the filter bacteria are retained in the filter.
When replacing activated carbon, rinse it with tap water to remove fine dust particles prior to placement in the filter.
Water Testing should be performed a series of water tests shows that the water weekly or monthly. This assumes ranges for each quality remains within” acceptable parameter. pH test is mandatory for all marine aquariums. A pH test will determine if the pH range is within 7.8 to 8.3. For the majority of marine aquariums, especially those with invertebrates, the pH should be maintained within 8.0 to 8.3. As discussed previously, the pH will decrease over time and hence must be monitored. If the pH has decreased, it will be necessary to make an immediate partial water change.
A salinity test should also be made weekly to ensure that salinity is within an acceptable range. If the salinity has increased, simply add enough fresh dechlorinated water to bring the salinity back to an acceptable level. As previously discussed, the salinity is determined by first testing the specific gravity using a hydrometer.
A nitrate test should also be made weekly. The accumulation nitrate is determined by many factors, including the initial number of fish and invertebrates in the aquarium, amount of food fed, type of filtration system, and extent of algae in the aquarium since algae utilize nitrogen compounds. aquariums with an abundant growth of  algae will not accumulate nitrate as rapidly as those with little or no algae. Excessive concentrations of nitrate in the “water.  While   not directly toxic, can interfere with the normal growth and longevity of marine fish and invertebrates- Invertebrates generally do not tolerate excessive concentrations of nitrate in the water.
Other tests, including those for carbon dioxide  and dissolved oxygen, are seldom required. Once the aquarium is functioning properly and has completed the conditioning period. The only exception that would necessitate more frequent testing would be if a substantial modification is made to the aquarium system, such as  the addition of a new filter, a complete cleaning of the systems, change in the type and amount of food fed, or the addition of several new fish.
General Fish Background Information
What is a fish?
A fish is a vertebrate, meaning it has a backbone.  It is also entirely aquatic with a few noteworthy exceptions.  These fascinating creatures can live in freshwater, saltwater or brackish water.
Basic Anatomy and Physiology
With ornamental fish we are concerned with four basic groups of fishes.
• Coldwater (ambient temperature fishes) freshwater
• Coldwater (ambient temperature fishes) marine
• Tropical (21-29 ˚C) freshwater
• Tropical (21-29 ˚C) marine
The saltwater fish presents a challenge with their tremendous diversity of shapes.  They all generally have similar organ systems.  Freshwater fish present more uniformity in anatomy.  In all fish, the bulk of the body consists of muscles for swimming. The coloemic cavity for fish is relatively small.
Integument
As with mammals, the integument provides the first line of defense against desiccation, disease causing agents, and some injury.  Most people recognize fish as a scaled animal, however some fish have scale modifications or no scales at all.  The scales (if present) sit in ‘scale pockets’ of the dermis and have a layer of epithelium covering them. Fish are capable of regenerating lost scales. Rough handling by netting can result in injury, which may result in bacterial or fungal infection.  There are also many external parasites that may afflict your fish. The gill cover (Opercula) also exhibits variations of particular note. In some saltwater fish, the opercula resembles more of a pore or tube, not the typical flap.  This is important when trying to identify fishes.
Gills
These serve a three-fold function of respiration, excretion and osmoregulation. Oxygen and other gases are adsorbed by the gills and carbon dioxide is excreted.  Oxygen diffuses much slower through the water than in air.  Therefore, oxygen is far less available to aquatic organisms than in air-breathers.  An increase in salinity and/or temperature will reduce the oxygen content of water.  The general gill structure provides a large surface area for gas exchange and a counter-current exchange that results in the availability of approximately 80% of the dissolved oxygen.  Ventilation in most fish results in a continuous flow of water across the gills.  In the first part of the ‘double pump’ respiration, the mouth is open and the opercula are closed which draws water into the oro-pharyngeal cavity.  The second phase occurs with the mouth closed and the opercula open to force water out.
Nitrogenous wastes excretion is the primarily the function of the gills, not the kidneys.  Up to 75% of ammonia wastes (main excretory product in fishes) are removed by the gills. Chloride cells in the gills are responsible for osmoregulation and mineral balance.  The gills can be damaged by excessive pH, high ammonia levels in the water and many types of parasites.  The response of gills to damage is by excessive production of mucous that inhibits gas exchange.
Swim Bladder
This is the glistening white sac in the retropertoneal dorsal body cavity.  The swim bladder is used as an equilibrium-ballast device.  In some fish there may be connections with the inner ear or distal esophagus.  Some bottom dwelling fish do not have swim bladders.
Gonads
Gonads will vary in size with the breeding condition of the fish.  The testes are generally white and smooth close to the distal portion of the large intestine.  In the gravid female, the eggs will fill a major portion of the coelomic cavity. 
Gastrointestinal Tract
The GI tract is similar to mammals with the length depending on diet type (herbivores, carnivores, or omnivores).  Herbivorous fish tend to have longer guts than carnivores.  In some species there are extensions there are extensions of the pyloric portion of the stomach called the pyloric caecae.
Liver and Gallbladder
The liver is yellow-brown to dark red in coloration and is multi lobed.  It functions as a mammalian liver does.  It will be involved in most systemic cleansing processes.  The gallbladder is a sac like structure embedded in the liver tissue. It may be small or large depending on the species and whether the fish has recently eaten.
Spleen
The spleen is usually bright red in color, species dependent on shape and usually located near the fundic portion of the stomach. It is the site of red blood cell production and storage.
Heart
In fish, the heart is two chambered, although there are four divisions.  The sinus venosus, atrium, ventricle, and bulbous arteriosus.  It is located cranial to the liver and adjacent to the gill (in the ‘throat’ of the fish).

I Bought What I was Told, Why Are My Fish Still Sick?
Successful resolution of an aquarium health problem involves one of the following:  either blind luck; or the fish would have recovered whether you did (or in spite of what you did) anything or not; or else a correct series of events involving diagnostic and treatment choices.  Since we can’t do much about the first two, I’m going to talk about the last one.
The steps involved in successful treatment of problems are:
1) correct identification of the problem
2) correct choice of therapy
3) therapy (such as drugs) contain sufficient active ingredient
4) therapy is actually getting to the pathogen, in sufficient quantity to kill it without being of harm to the patient
5) problem is treated for adequate length of time
6) conditions are optimized for the patient (this is not absolutely necessary but will definitely increase your chances of success)
As you can see, this makes the whole thing a little more complicated than it seems on the surface.  I’m going to discuss each of these points in more detail.
1) Correct identification of the problem.  This is WAY harder than you might imagine.  Many things look like many other things, and especially when one is going by a description given by another person, it’s difficutl to be accurate.  Access to a microscope and a book with good pictures helps; also, common things are common (that’s why most people can identify ich, for instance).  Not all red streaky fins mean septicemia, though, and not all cases of septicemia are caused by the same bacteria.  So if a disease isn’t responding as expected, the first step is to rethink the diagnosis.
2) Correct choice of therapy.  This step contains several implications – that it has any effective therapy at all, or that this particular strain is susceptible to the same things the usual strains are.  Bacterial infections, particularly in freshwater aquarium fish, are becoming increasingly resistant to the average antibiotics used (and this is partly the fault of being bombarded with antibiotics on a random basis).  Aeromonas and Pseudomonas, for instance, are common pathogens, and are notorious for developing resistance to drugs.  You might read in a book that most bacterial problems in fish are caused by Aeromonas, and that Drug  So and so kills it, but that may no longer be the case. 
3) The therapy you have now acquired is actually any good.  If you’ll notice, treatments (especially antibiotics) are labeled “for ornamental fish use only”.   There’s a good reason for this – the purity and strength of the drug may not be being monitored particularly closely, and indeed it’s possible that it is outdated or contaiminated. 
4) Proper delivery mode and adequate strength.  By and large, treating an internal infection (such as septicemia) with an external bath (putting meds in the water) is useless.  The fish’s skin is designed to keep foreign substances out, and the therapy simply isn’t getting to where the problem is.  Either buying a prepared medicated food or making your own (if the fish will eat) is more likely to be of help.  An exception to this is certainly problems like flukes, or columnaris while it is still external; baths may well help here.  As for adequate strength – commercial preparations are made with the idea of avoiding problems associated with overdose, so they are deliberately made to dose on the low side.  This may well be inadequate for treating many problems.  And realistically, little is known about adequate dosing in fish – absorption, drug breakdown, drug toxicity is probably different from species to species, and very little is known in non food type fishes.  Things tend to be extrapolated from trout and catfish  and salmon, and may not be truly valid.
And some things work just fine, but can be toxic easily – formalin (formaldehyde solution) is a good example.  It’s a pretty effective killer of many bad things, but unless used very carefully, can be pretty hard on the fish (the environment as well).  So you really have to know what you’re doing to use it.
5) Problem treated for adequate length of time.  Often, the signs go away, but some of the bad guys are still present; if treatment is stopped too soon, they can come back with a vengeance (since it tends to be the sturdier one who are killed last).
6) And finally, the fish with the immune system that is functioning at its best will have the best chance of getting it over the problem.  Optimal living conditions will help the immune system. 
So, as you can see, a failure in one of these steps will lead to treatment failure.  Develop a systematic way of looking at problems and formulating a treatment plan, and you will have the most likely chance for success.