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Fish Diseases II - Diagnosis and Possible Cures

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As usual, avoiding problems is always better than fixing them. All in all, the less stress put on your fish and the better your maintenance regime, the better your chances of having happy, healthy, long-lived fish. Keep all equipment clean, do not over-clean filters, do not over-populate, feed sparingly, perform good quality water changes regularly, etc etc etc. But, if your fish do become infected with a disease after all, here's a list to help you identify it and and try a cure:

White Spot (Ichthyophthirius)
A parasite that we will all encounter whilst keeping fish. As an adult, it is embedded in the skin of the fish causing irritation. Your fish will probably be glancing off rocks and plants to alleviate the itching. The parasite will feed and grow on the blood and skin cells of its host for a few days, until it is fully grown. It then bores its way out of the skin and drops off into the substrate. It then forms a cyst which goes through rapid cell division until about 1000 young are released into the water to start the whole process again. The whole process takes just five days at 27°C. There are cases where the parasite actually lies dormant in the skin of the fish and will not emerge until it is ready, making eradication quite difficult. The best time to kill them is when they are free swimming and looking for a host. Treatment must be external and aimed at the free swimming stage, hence the need to dose again after a few days. Suitable cures are widely available.

Velvet (Oodinium)
Velvet is caused by a dinoflagellate, classified by some as an alga because it carries Chlorophyll. There are two main species, Oodinium limmneticum and Oodinium pillularis. The free swimming stage of Velvet settles on the skin and gills of the fish, adhering at first by its long flagellum, later putting out pseudopodia, (similar to fingers) that penetrate the skin and give it a very firm grip. Velvet has a similar life cycle to White spot: feeding and becoming a cyst, it produces upward of 200 young before dropping off. The appearance is similar to gold or brown dust over the body and fins which at times may appear to move. Symptoms are similar to White spot, glancing off rocks, etc. As Velvet is highly contagious, it is important to eradicate this problem as soon as possible. Treatment is aimed at the free swimming stage and there are good cures available from your local store. Copper sulphate can be used at a concentration of 0.2 mg/L or ppm. This should be repeated after 3 days to ensure eradication.

Fungus (Saprolegnia or Achyla)
Fungi are in fact colourless plants, they are very diverse in form and have not been studied that much in fish. Saprolegnia and Achyla are genera of fungi that attack weakened and injured fish, usually settling on damaged skin or gills. They will also attack the eggs of fish. The spores enter the aquarium from the air so there is no way to stop possible outbreaks. Threads of fungus spread under the skin forming a web like structure and eventually produce tufts of external hyphae that may be large enough to look like cotton wool. These form spores that become free swimming and can then go on to infect other fish that are weak or injured. It is important that you remove any fish you suspect immediately to a hospital tank for treatment. Symptoms of fungus are a grey or whitish growth in the skin of the fish, often associated with visible damage. Treatment can be with Malachite green in a separate tank for 30 seconds at a strength of 60 mg/L. Repeat treatments may be necessary. The fungus is stained by the Malachite and usually drops off within a few hours. Keep the fish under observation for 2 or 3 days as fungus can sometimes regrow.

Mouth Fungus (Columnaris)
Although Columnaris resembles fungus it is in fact a Bacterium. It is usually found just around the mouth area, rarely spreading. The first signs are a thin white line around the lips, which then grows into white or grey short tufts that resemble fungus. Early treatment is needed if you are going to save the fish's life, due to the toxins released and the fact that the fish cannot feed. The best and most effective cure is to use Anti-Biotic. Penicillin is very effective at 10.000 units/L, with a second dose after two days. Remember to remove all filtration whilst dosing to avoid killing the beneficial bacteria.

Neon Disease (Plistophora)
Named after the fish that it was first identified in, but this problem can affect all other tetras and it is now known to affect other species. The organisms lie in the muscle tissue in the form of cysts which burst and release spores, the spores then bore deeper in to the muscle and then repeat the process. Eventually some of the spores will reach the water, probably via the gut. These then go on to infect more fish, usually by ingestion. I personally think the best way to control this is to humanely kill the infected fish as there is no reliable cure.

Digenetic Flukes (Metacercaria)
Typically seen in newly imported fish and in two forms. Black spot is caught from snails that release the Cercaria. Larval forms penetrate the skin and encyst in the tissue and may be seen as red or black nodules. If eaten by a Bird for instance they then develop into adults. Sanguinicola disease passes from fish to snail and then back as minute worms that live in the fishes bloodstream. There they lay eggs that block up the blood vessels which in turn causes Necrosis. As far as I know there is still no cure for this problem.

Tapeworm Larvae (Cestoda)
Not commonly seen in fish, but can be introduced in tubificid worms as food. They then become adults in the gut of the fish, usually about 3mm in length. Not seen very often in the aquarium, but if seen there are commercial cures available, best to consult a Vet.

Costia
Costia necatrix is rather rare in aquariums, but if seen as skin cloudiness is easily eradicated by raising the temperature to 32°C, otherwise treat as Velvet.

Chilodonella, Trichodina
These actually sit on the skin and are more easily eradicated. Usually spotted by the fish glancing off objects, clamped fins and gasping at the surface as the gills are often infected. Treat as Velvet.

Red Pest (Bacterial)
Red pest is so called because of the red streaks that occur on the skin, that may lead to ulcerations, and fin or tail rot, causing parts of the fins or tail to actually drop off. This bacteria infects the fish internally and externally, and treatment is not usually effective. If fish are only lightly infected you can try to eradicate this problem by sterilising the aquarium with Acriflavine or Monacrin. Giving the aquarium a good clean up is also helpful, feed lightly whilst treating. Personally I would not bother with treatment as by the time you notice this bacteria it is usually well advanced, and the fish are already suffering.

Fin Rot (Bacterial)
Usually the secondary stage of Red Pest (above). Several bacteria can cause it. If the fish reaches this stage then you will have to use Anti-Biotic to eradicate. Remember to remove all filtration as the Anti-Biotic will kill the beneficial bacteria. Typical symptoms are: discoloration of the fins (in early stages may go unnoticed), fins become ragged and frayed, and in terminal stages only shreds of the fin or tail remain. Can lead to secondary fungus infections. The main causes are improper maintenance routine, infrequent water changes, temperatures too low for the fish being kept. This is a highly contagious disease.

Ichthyosporidium
This fungal disease is widespread, attacking the liver, kidneys and pretty much everywhere else. Infection begins via food and the parasites infect the blood stream, settling down as brown cysts. These then grow and produce daughter cysts by budding or by the mother cysts bursting and releasing the young. The symptoms depend on what part of the body is infected. Fish may become sluggish, show hollow bellies, lose balance, and eventually external cysts and sores. By this time it is usually to late to save the fish. Treatment is difficult, but treat as for Saprolegnia.

Pop-Eye (Exophthalmia)
Pop-eye may not be caused by infection and there are various causes. Easily identified by the protrusion of one or both eyes. It is commonly caused by excess gas in the system, brought about by super-saturation of gas in high pressure water mains. It can also be associated with Dropsy or Ichthyosporidium. Look for bubbles of gas in the eyes, this indicates the bends, as does nervous upset, distress or just odd movements. If these signs are obvious then lower the temperature slowly to increase solubility of the gas (usually nitrogen) reduce aeration and wait to see if there is any improvement. In marine aquaria, copper poisoning can be one of the causes. Pop-eye can also be caused by hormonal imbalance, for which there is no cure.

Hexamita (Hole in the Head)
Usually associated with Discus, this Flagellate will in fact affect other fish, particularly large cichlids. Hexamita infects fish by ingestion of food and begins life in the gut. Infected fish will usually appear thin in the stomach and may have sores or ulcers around the head. A bad case looks as if someone has chiselled out holes in the head. It is said by some that this will cure itself by generally cleaning the aquarium and paying extra attention to cleanliness and good quality water changes. There are cures available from your Local fish store.

Argulus, Ergasilus, etc
Fish lice (Argulus) are in fact a small crustacean that attaches itself to its host and then proceeds to feed on its blood. It is thought that they can transmit disease, so should be removed quickly. On large fish this can be done with forceps, unless you have a mass infestation. Potassium permanganate in a hospital tank at 10 mg/L for 10 to 30 minutes is effective. Or, alternatively, you can use insecticides but I am not sure about the use of insecticides in the aquarium. I personally would try a salt bath first to see if they drop off. Ergasilus is also a crustacean that affects the gills of fish. Try the above cures or ask for help.

Gyrodactylus Monogenetic Flukes
In fact a flat worm that in the early stages can be mistaken for white spot. They infect the gills and skin of their host and produce live young. Symptoms are pale skin, drooping fins, rapid respiration and even emaciation. Treat as for Argulus, Potassium Permanganate or alternatively use Formalin, but only in a hospital tank. Use 2 ml of 40% solution per 10 litres for 45 minutes. Salt bath at 15 g/L for 20 minutes may also work.

Nematodes
These threadworms will infect all parts of the body, but are only seen when hanging from the anus of the infected fish. Consult a specialist, or personally I would consult a Vet. There are theories that threadworm treatment for cats can be used mixed in with food, but I do not know the amounts needed.

Lymphocystsis
A viral disease that causes the host cells to swell up giving rise to tumours, that almost look like spawn (granular) attached to the body and fins. There is no guaranteed cure so it is probably best to euthanize the fish.

Glugea, Henneguya
Sporozoans that form large cysts that look similar to Lymphocystsis and is also incurable. Dispose of the fish humanely.

Tuberculosis
Symptoms are Hollow belly, Knife back, Pale skin, Bending of spine. They also lose their appetite which does not help them. If suspected, it is best to dispose of the fish immediately. Tuberculosis can be passed on to humans, but only if you have open wounds on your hands when placing them in the aquarium.

Trynoplasma
Sleeping sickness infects the blood just as it does in humans. Infected fish are drowsy, may swim strangely and become thin. It is usually seen in pond fish that have been recently moved into an aquarium. I think it is brought on by warming up the fish too quickly. There is no cure.

Dropsy (Aeromonas)
Dropsy usually takes one of two forms: body swells due to fluid accumulation, which causes scale protrusion, and also protrusion of the scales without the body swelling up - false dropsy. Dropsy is caused by a bacterial infection of the kidneys and other internal organs, causing fluid accumulation or even renal failure. Treatments are varied, adding salt at a rate of 20 mg/L seems to help. With modern Anti-Biotic this problem can be cured.

Reader Comments Comentário

I would like to point at that aquarium salt shound NEVER be used for Dropsy, it kills them instantly. Fish cannot expel salts and water and the added salt makes it worse. You should advise Epson Salt, this extracts fluid from the skin. I tried the advice of aquarium salt and my fish died within 5 minutes. Hope this will help others.

Contributed by Caroline Worthington

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