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The clinical signs of fish disease that can be directly observed by the eye are generally quite indicative of the disease group. For example large ulcers often indicate bacterial infection; spinning may indicate a neurological disorder or flicking off surfaces may indicate a parasite infestation. However, fish diseases often have clinical signs that can be easily mistaken for a number of diseases. For example, dropsy is a term used by many hobbyists for any coelomic swelling. However, it may be caused by acute liver failure, liver carcinoma, kidney failure or infection, gill, intestine or skin damage, a viral infection or bacterial septicaemia. Hence, the presence of the symptoms of dropsy may indicate a range of both infectious and non-infectious problems.
Under suitable aquarium conditions, healthy rainbowfishes display "normal" behaviour. As an aquarium hobbyist, you should become familiar with the normal behaviour of your fish. If their behaviour changes; for example, they stop feeding, swim near the water surface, dart, or scratch on objects, then something has occurred and you need to find out what. The cause may vary considerably, from stress due to their aquarium conditions or symptoms of specific diseases.
Following are examples of the most common symptoms:
- Abnormal swimming: Fish staying relatively still in one place in the aquarium, often accompanied by shimmering or shaking. Swimming in an oblique position with the head directed toward the surface. Continuous swimming to and fro, following the same path (or several similar paths), from one point of the aquarium to another. Staying put at the bottom of the aquarium for unusually long periods of times.
- Aggression: Fish showing repetitive hostile or violent behaviour towards another individual/s. Some territorial fish or breeding fish may show this aggression naturally, but its intensity and frequency may be modified (increased or reduced) if the fish is stressed or sick.
- Colour change: Changes of body colour that do not match the expected changes due to maturity, courtship or reproduction. This may involve a fish becoming dark in colour or lost of colour, with decreasing intensity over the entire body.
- Fish stop feeding: Fish often stop eating as a disease progresses.
- Flashing: Every now and then an individual will swim towards the bottom and then suddenly move forward, turning on one side and appearing to rub one flank on the substrate or some other object. Generally it is a sign of ectoparasite infestation. Parasitic infestations are diseases, and flashing is a response to ectoparasites to get rid of them. Usually the flashing fish will flash repetitively as opposed to just once. There is another possibility besides the ectoparasite infestation. It is well know that poor water quality can also be the cause of flashing behaviour.
- Gulping: Gulping of air at the surface of the water and rapid breathing.
Most of these behaviours, however, are difficult to assess based on a quick glimpse of the individual fish in the aquarium, and it is only as effective as the skill and care of the person carrying it out. It is difficult to recognise a change in colour of a fish if one has not seen its usual colour, or it is difficult to identify a case of abnormal swimming without knowing the activity pattern of that particular individual. Many of these behaviours may be quite subtle, and only the accustomed eye of the experienced aquarist can detect them.
© Copyright Adrian R. Tappin
Created July, 2005
Updated December, 2008
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