Other Causes
There are of course, many other reasons why disease may take hold in the aquarium. The most common of these are listed below.

Low genetic immunity
Intense breeding programs which are used to develop colour or finnage strains require closely related fish to be bred together and offspring to be separated and isolated in order to pick the desired types for further breeding. This activity reduces the fish's genetic strength, natural immunity, and ability to deal with pathogens. A low genetic immunity causes a fish to be prone to infections, which the fish cannot fight, and is quickly overcome and often dies.

Incorrect diet
Like other complex animals, fish require a wide range of vitamins, nutrients, and minerals in order to survive and grow in a healthy manner. Correct feeding requires all these needs to be met as well as a correct frequency, amount, and avoiding excess. Incorrect diets will cause a weakening of the immune system, physical deformities, and excessive stresses on internal organs often leading to early death.