It is important to observe your fish. Most fish will tell you when something is not right by their behaviour or appearance. They may look off colour, act listless or behave erratically. At this point one should look closely at the fish for visible signs of infection and ascertain any remedial action. It is usually fruitless to try and diagnose a source of infection from a dead fish and then to introduce a preventative cure for the remaining fish. At tropical temperatures, fish decompose rapidly and most parasites will leave a dead fish quickly.

It is equally important to fore see signs of trouble from your aquarium condition. Rotting food remains, black patches appearing on sand and yellow water all indicated that tank maintenance are long over due. It usually when conditions deteriorate that fish become weakened and susceptible to infection and disease.

No medication should be used without understanding the cause of the disease. Disease will often reoccur if this step is not carried out. Most outbreaks of disease are due to environmental factors. Don't think of yourself as a fish keeper, but as a water keeper. Often, if one can look after the water, the fish will look after themselves. If disease does occur check your water quality first. (Take a look at the Water Chemistry and Aquarium Maintenance sections). Also look at possible sources of infection from less obvious sources such as feeding live Tubifex worms or other external factors like a draft from a door or window which can often be the cause of sporadic outbreaks of White Spot (Ich).

The table below is affords to help diagnose the most common diseases that can be seen with the naked eye. It also provides links to an explanation of the disease and a suggested course of treatment. Whilst this may not enable a precise diagnosis, it may narrow down the causes of infection to allow treatment or prevent reinfection. Please do not treat any fish unnecessarily and ensure that you have positively identified the disease before administering any medication as some symptoms may indicate more than one possible disease. If in doubt consult a veterinary surgeon.