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Fish Disease Handout

Bob Fenner  

Effective Retailing: Useful Handouts

This is another in the series of handouts we've found to be useful in supplying our customers with a ready reference of  necessary information. We distribute these freely at our retail outlets and public shows, printed on our company stationery with business cards attached. We have found them to be an extremely effective form of advertising and promoting the hobby.

Fish Disease Handout

Baseline knowledge of disease prevention, recognition and treatment is essential to keeping your fish healthy. This handout will provide you with a standardized, reasonably complete, concise understanding of fish disease.


Disease is "any deviation from a normal or healthy state." There are many ways to describe/classify types of disease; genetic, nutritional, developmental, viral, bacterial, parasitological, environmental, et al., depending on the perceived causative factors. It cannot be stressed too much that all disease is environmentally, and especially, "water-quality" mediated.


Prevention is always the best medicine. In an aquarium, there are three areas of prevention: stress, fungus and bacteria, and parasites.

To overcome stress use a good conditioner like Novaqua or Amquel. This will neutralize chlorine, detoxify some metals, and provide an extra slime coating for the fish. If a chlorine neutralizer is not wanted, use Polyaqua.

To prevent fungus and bacteria infections, add about a tablespoon of salt per gallon to a fresh water tank. If live plants will be in the tank, use only a half dose. To prevent fungus and bacteria in a salt tank, use freshwater and formalin dips when introducing livestock and/or quarantine, frequent water changes, ultraviolet sterilizers, ozone generators, and protein skimmers.

For parasite control use copper. In a freshwater tank use Aquarisol and shimmy blocks. In saltwater tanks use a good liquid copper solution or a good copper/formalin solution and copper (Shimmy) blocks. When using copper as a preventative use only a minimum dose, (5 days of Aquarisol or .15 ppm copper, formalin for one day- skip one day- then once more.) Do not use any copper with invertebrates!. Use Tetra medicated food when introducing new fish or when invertebrates are present.

If fish still become sick, check for possible causes of stress and eliminate it if possible. Identify the disease and treat accordingly. Treatments should be recorded on the tank and/or in a log.


Any tank condition that is not good for the fish may cause stress and stress usually leads to disease. The most common sources of stress are: 

1) Improper pH or drastic and\or sudden changes in pH

2) Improper temperature or sudden changes in temperature.

3) Improper salinity for extended periods.

4) Improper hardness, or sudden changes in hardness.

5) Pounding on tank, or sudden movements that scare the fish.

6) Aggressive tankmates.

7) Poor diet. Too little, too much, wrong foods, wrong time.

8) High nitrite levels. (A high nitrite level prevents oxygen from reaching the cells and may cause suffocation or brain damage).

9) High nitrate levels. (This may lower the pH as well).

10) Any measurable ammonia level. (80% of all fish waste is in the form of ammonia and is extremely toxic if not converted immediately into nitrite).

11) Other toxins. (Chlorine, copper, detergents, iron, lead, zinc, cleaning ammonia, nicotine, perfume or

cologne, oil, paint fumes, insecticides including contamination from dog and cat flea collars, etc.) 

12) Too little or too much dissolved gases, or a rapid change from water that is saturated with gases to a normal level. This can be a problem when releasing newly arrived fish into the aquarium. If the water is not mixed, the fish may suffer a condition that is very similar to "the bends" suffered by SCUBA divers and may be just as deadly.

13) Too much or too little light. Too much light, no, or short periods of darkness, speeds up the metabolism of the fish and does not allow the fish to rest. Too little light and the fish may be lethargic and not eat properly.

14) Dirty or cloudy water. Cloudy water is usually caused by bacteria. The bacteria in the water uses all the available oxygen and the fish suffocate. Microbes may produce toxic metabolites, resulting in "mysterious' losses or the so-called "wipe-out" syndrome.

15) No hiding places for the fish to feel safe. 

16) Loss of mucus of the fish's slime coating. This condition may be caused by stress instead of the other way around, but once the slime coating is lost, additional stress is incurred.

17) Infectious, Protozoan disease. 

18) Any other sudden changes in the environment. 

19) Overcrowding. Inappropriate sex, size ratios. 

Stress triggers the release of epinephrine (adrenalin), a hormone which tells the fish to get ready to fight or flee. This increases the heart rate, blood pressure and respiration. At worst, continual stress will cause a fish to die of exhaustion. At best the fish becomes so weak his immune system no longer functions and he dies from a disease that would not kill an unstressed fish. A stressed fish usually becomes sick. If the stress is severe the fish may go into shock and die immediately.

Most aquariums have a constant supply of fungus, bacteria, and parasites that have little or no effect on a healthy fish. Once a fish is under stress however, it does not have the ability to fight the infectious organisms and falls prey to the first disease organism that comes along.

Fish and invertebrates are more dependent on their environment than any of the higher animals. They are totally dependent on their owners to provide them with proper living conditions.


ICH- Think of ich (Ichthyophthiriasis), white-spot disease of freshwater fishes as an army of individual animals living off the juices of the fish. These are visible as pinhead spots on the fins and bodies. While on the fish they are usually encysted and protected, and cannot be killed until they drop off the fish to reproduce on the tank bottom. Therefore treatment must continue through the entire life cycle of the parasite which usually is about 4 to 5 days. A low temperature can slow the cycle down to 6 or 7 days. A high temperature can speed it up to as little as 3 days. A high temperature (85 degrees or more) can kill parasites by itself but may also kill the fish or add to the stress of a fish with parasite choked gills. 

Any parasite infection is usually easy to cure if treated quickly with an effective dose of copper. If the dosage is too low, not all parasites are killed and re-infection results. If treatment is delayed, the parasites may become so numerous that they choke the gills and the fish suffocates or the fish becomes so weak it cannot recover. Treatment should continue for at least 4 days and a good rule of thumb is to treat the tank every day until no sign of infection is visible, then treat one more day.

Each parasite leaves a wound where it was attached to the fish. These wounds are easily infected by bacteria and an antibiotic should be administered following the copper treatment. Marine fish should be dipped on arrival to prevent Cryptocaryon.

Copper treatment in a marine tank can be a tricky thing and should be used with the aid of a copper test kit. To be effective .25 to .30 ppm of dissolved copper ion must remain in the water continuously. The problem is that dissolved copper is readily absorbed by gravel, rock, and coral. In a new marine tank, dissolved copper seems to disappear almost as soon as it hits the water. This makes it difficult to keep an effective dosage in solution. After several treatments, everything in the tank becomes saturated with copper and will no longer remove the copper from solution. At this point it is very easy to overdose.

If too much copper is used it may be toxic to the fish. Fish previously treated with copper become more tolerant of later doses while previously untreated fish may die from the same dose. Proper use of a copper test kit allows you to monitor copper levels for effective treatment. Copper levels may be changed by the pH of the tank, staying in solution longer at a high pH. It is possible to maintain a safe copper level at a low pH and increase the copper to toxic levels by doing a water change that significantly raises the pH of the water and releases absorbed copper back into solution. Chelated copper will remain in solution longer than ordinary copper sulfate. Always use high quality copper to avoid contamination from other minerals that may prove to be toxic. It is necessary to remember that the copper absorbed by the substrate may prove fatal to invertebrates months or even years later.

Polyfilter and types of activated carbon (e.g. Chemipure) will remove copper from the water and should be removed during treatment. Some high quality carbons may remove copper, but are not usually strong enough to make a great deal of difference during treatment.

A shimmy block is copper in a solid state that gradually dissolves and releases copper into solution. They can be especially effective in saturating a new tank with copper. Tetra medicated food, flake "D", is highly recommended in conjunction with copper, and in a tank with invertebrates may be the only available treatment. (Copper kills invertebrates).

A low salinity is damaging to marine parasites and most tanks will benefit if a range from 1.017 to 1.019 is maintained. A low salinity is not recommended for invertebrates however.

Signs of a parasite infestation are:

1) Visible spots, usually white, that make the fish look like has been salted or covered with powdered sugar.

2) Rapid or heavy breathing. Some parasites will attack the gills before any can be seen on the fins or body, and the fish may die from suffocation.

3) Scratching. If a fish constantly rubs against objects in the tank and looks like he is trying to dislodge something, he is probably trying to rub something off and it is usually a parasite.

Because ICH reproduces in the gravel, the whole tank must be treated, not just the infected fish. Hospital tanks and dips seldom effect a permanent cure, and cause a great deal of extra stress for the fish. Ich infections may produce an immunity to later attacks.

Malachite Green is effective against parasites but may damage gills and\or chemically "burn" tetras and scaleless fish. Malachite Green that is not pure is especially dangerous.

Dylox is effective; it is an insecticide and usually is not toxic in recommended dosages.

OODINIUM/Velvet- This is actually a form of algae on freshwater fish. In a marine aquarium it is the salt water version of

velvet Treatment is described under ICH.

ANCHOR WORMS- These are easily visible and look like little sticks about 1/4" long protruding from the body or fins. They are firmly attached and when pulled out may hold onto a piece of flesh. Medicated food, flake "D" and Dylox is the recommended treatment and it usually takes 10 to 14 days for full eradication. After a few days of treatment, any remaining worms should be removed from the fish. Because of the large sores left by the parasite, fresh water and an antibiotic is a must during and following treatment with Dylox and flake "D".


This is a virus that lives off of impurities in the water while attached to a fish. It does not live off the fish (like ICH), but may kill indirectly by interfering with gill movement, swimming ability, or eating. Lymphocystis can only be killed in the aquarium by removing its food source by means of purifying the aquarium water. This can be done with ultra-violet sterilizers, ozone, chlorine, frequent and large water changes, micron filtration, or diatom filtration. In the late stages of successful treatment, the virus clumps may be easily removed from the fish by scraping with your fingers, or may drop off as it dies.

The virus itself cannot be trapped by filtration, only its food source can be removed. Lymphocystis virus transfers easily between species but less easily between genera. The more densely populated an aquarium, the more easily the virus may transfer from fish to fish.


Bacteria grows erratically and the infection is often white or milky in appearance. A bacteria infection may be localized or may be evident on several areas of the fish. Bacteria infections are likely to be found in or around open sores or any area where the fish has lost it's protective slime coating. 

Antibiotics and medicated food should be used to treat bacteria infections along with frequent water changes. A dirty aquarium can prevent successful treatment. Because there are so many different types of bacteria, you may have to try several types of antibiotics before finding one that works. Be sure to do large water changes between treatments of different medications. Good quality carbon or charcoal, Polyfilter, and Chemipure, will all remove medications from the water and should be removed during any treatment with antibiotics. 

Internal bacteria infections are identified by the gas they produce. This may cause the following symptoms- swelling, a fish that has trouble staying on the bottom, whitish feces that float or trail off behind the fish, or lack of feces entirely (blockage).


Fungus spreads evenly, starting from a central point and growing in an outward pattern. Several areas may grow outward until they overlap and give the appearance of a bacteria infection. Fungus is white with a velvety or even hairy appearance. It is most likely to be found on the mouth, eyes, or tips of the fins.

Treatment consists of water changes, medicated food, and antibiotics. Triple sulfa is usually the best treatment for fungus. Salt by itself may effect a cure. See above for dosage.


This is a symptom, not a disease. It is usually caused by swelling behind the eye (or in the eye). The swelling may be caused by many factors but is most commonly caused by bacteria. 

If unilateral (only one side) the cause may be mechanical injury. Time only may effect a cure. It is difficult to treat, but the most effective procedure seems to be a good environment, and medicated food. Start with flakes "D" and "A" in conjunction, then feed flake "B", and go on to flake "C" if needed. Erythromycin or Chloramphenicol may also be effective.


The swim bladder is the organ which allows a fish to stay at any level in the aquarium without sinking or floating. The swim bladder may fail from damage by bacteria, parasites, genetic faults, or blows and/or bruises. When the swim bladder fails to function the fish loses it's ability to swim normally and may swim sideways or even upside down. Once damaged, the bladder does not usually return to normal functioning, but if the fish can eat and swim without too much strain it can live for years with the condition. Goldfish seem particularly prone to swim bladder problems. Without knowing the exact cause of the malfunction, treatment is difficult. Since internal bacteria, fungus, or parasites are the only treatable causes, medicated food and/or antibiotics should be tried along with frequent water changes.


Dropsy is a name given to any disease that causes a fish to swell so much that the scales no longer lay flat against the body of the fish. By looking down on a fish you can easily spot a case of dropsy. This is a very difficult condition to treat successfully. Daily doses of erythromycin, daily water changes, and exclusive feeding of medicated food ("D" & "A") has proven to be the most effective treatment. Including regular feedings of daphnia may prevent some cases of dropsy. Goldfish, Gouramis, and guppies (in that order) have the most trouble with dropsy but it may be found in any fish.


Rapid breathing or gulping near the top of the tank may mean a fish is not getting enough oxygen. This may be caused by:

1) No air circulation. Air pump or stones may be faulty or missing. Surface agitation may be missing in a "system" tank.

2) Temperature is too high. The warmer the water, the less oxygen it can absorb and hold.

3) The water surface is covered. Water cannot absorb oxygen if the surface is covered with scum or if the water level is so high that it touches the top.


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