Fish disease diagnosis

Don't just guess what the problem is!

Let me say right from the start that it is just not possible to diagnose fish disease and health problems without first examining the affected fish and possibly the fish’s environment. After all, would you trust a doctor who told you what was wrong with you without asking any questions or carrying out any examination?  Would you phone up your vet and expect him to tell you over the telephone what was wrong with the family cat or dog?

Obviously the answer to both these questions is no.

Trying to guess what is wrong, (and that is all that people do if they don’t carry out any investigation), is obviously the wrong way to go about things, unless of course you believe that aquarists and dealers have some form of mystical powers not possessed by vets and doctors!  Common sense and our own experience tell us that the right way to proceed is to establish what is wrong and why, before we carry out any treatments.

Detective work

It is important to realise that fish are aquatic animals and can be affected by most of the diseases that typically affect other animals, as well as diseases and health problems that are exclusive to an aquatic environment. However, unlike most terrestrial animals, they have a limited response to disease. For example, you will not see a fish holding up a sore fin, or limping or even whimpering. Their response is limited to refusing food, lethargy, jumping, rubbing or flashing, gasping at the surface and isolating themselves. There may be minor variations, but essentially these are the only ways that they can let us know there is something amiss.

The main point is that they will exhibit some of these signs irrespective of what the problem is. So we see the same responses to poor water quality, gill disease, parasites, heart problems etc. Given that they will respond in much the same way, irrespective of the cause, it is simply impossible to make a definite diagnosis based purely on behaviour.

Trying to determine what is causing the problem is a little like detective work as there are so many probable causes. Behaviour is just one small part of the puzzle. The initial aim in diagnosing health problems is to collect as much information as possible. When we have this information we can then make a balanced assessment of both the problem and the likely cause.

What information do we need?

Table 1 shows the most basic necessary information needed when investigating health problems:

With all of this information regarding the physical condition of the fish and the environmental conditions it is, in most cases, possible to determine both disease and the cause. From this we can decide what actions and what treatments are needed.

If this basic examination is inconclusive it may be necessary to carry out further investigation which could involve post mortem investigations of recently dead fish, bacterial sampling from lesions to determine the type of bacterium involved and their antibiotic sensitivity, histological examination which involves preparation and examination of body tissues and organs for signs of malfunction and disease.

Although this may all look involved and unnecessary the success rate of this type of methodical approach to fish disease diagnosis is far, far higher and usually a lot cheaper than either guessing or making simplistic diagnosis that only treat the obvious effects and not the cause.