I've been working on a photo archive of fish diseases that people send me or allow me to use from their sites. This list and archive of photos is not meant to be exhaustive or comprehensive. Please note also that some diseases have multiple manifestations (Columnaris, NTD, Fish TB, to name a few), and may vary in presentation from fish to fish; others are not true "diseases" caused by a single organism, but rather signs that could point to a number of causative organisms (dropsy, pop-eye). Click on the thumbnails, and you will be linked to the larger photos (if it was larger to begin with, that is, I can't enlarge photos any larger than they were when sent to me, because this will not improve resolution).
> is a common viral disease in both marine and freshwater fish. The commonly affected fish are cichlids and gouramis. is not infectious in nature. It mostly develops as a response to poor environmental conditions. Poor aquarium conditions, especially water quality, is held responsible for initiating . The affected fish develop wart like growths on its fins. These growths often have light brown coloration and a rough, cauliflower like texture. Another common viral aquarium fish disease is Dwarf Gourami Iridovirus (DGIV). The diseased fish show discoloration of the skin, loss of appetite and reluctance to move. It may or may not develop sores and lesions on the body.
The main defences against fish diseases are, quality control of the habitat they live in, this includes filtration, oxygenation and a well balanced diet which then lowers stress levels.
> There are some non-infectious aquarium fish disease. They are caused by environmental, nutritional and genetic factors. Some of the environmental factors are high amounts of ammonia, high levels of nitrite, low level of oxygen or toxins in the aquarium. The main nutritional factors leading to diseases is deficiency of vitamins like vitamin C. Genetic abnormalities include lack of a tail or presence of an extra tail.