Tropical Fish Disease


An important aspect of aquarium and tropical fish keeping is that of diagnosing and treating tropical fish disease.  This is an area that is often misunderstood, and under-studied by the average aquarist.

Most aquarium fish come from the tropics, where they live in extremely clean waters with low hardness, high oxygen content, and often with many dissolved organic substances.  Nutrients and elements are constantly replenished by mother nature.

Today, while it is quite possible to chemically adjust aquarium water to match the fish's natural waters, it is hardly possible to approach their degree of cleanliness.  This is simply because of the very small volume of aquarium water.

In nature a fish has huge quantities of water in which to feed and leave its droppings.  In the aquarium, however, fecal dilution is quite limited.  The more the fish swims in the aquarium, the more burdened or polluted the water becomes.  Polluted water harbors chemicals and microorganisms that are harmful to the fish.  Many of these microorganisms are parasites, bacteria and fungii that live throughout the aquarium, but they also can cause rapid depletion of the health of the fish, and disease.

In the wild, where the fish lives in large quantities of water, it is not often confronted with such organisms.  The fish can easily ward off an infection.  In the closed system of an aquarium, however, the disease-causing organisms multiply.  The fish is constantly picking them up, and its body, to a certain extent, is continually attempting to stop these organisms from multiplying in and on it.  The fish easily succeeds in resisting them if it is fed well and if it feels at home in its aquarium.  This involves proper water quality, aquarium maintenance, filtration, landscaping, and compatibility.

With good hygiene, you can make it tough for the disease-causing organisms to survive.  Immediately remove any dead or sick fish.  Regularly gravel vacuum out any accumulations of debris from the bottom crevices and from the nooks and crannies of any decorative items in the landscaping.  Change the water regularly.  Adjust water parameters regularly, and properly. Replace the bulbs on the light when necessary.  Proper aquarium maintenance is key to keeping the fish healthy.  For more info, see the Aquarium Maintenance section.

Just as in waters in the wild, the aquarium also has a biological self-cleaning cycle. You must recognize and foster this process in order to effectively care for the water in an aquarium, for, as indicated above, it has a direct relationship to the health of the fish.  There are many books on water chemistry and aquarium hygiene.  The better this process of self-cleansing is achieved--keeping the water quality high for longer periods--the rarer will be diseases in the aquarium. (Untergasser, Handbook of Fish Diseases, 1989)

This section is dedicated to the aquarist who wishes to dive into the intricacies and science of treating an array of tropical fish from many common diseases.

To the right is a menu of web pages for information on tropical fish diseases.

Disease Diagnoser

A step by step diagnoser for common freshwater and marine fish diseases.



A list of many freshwater fish diseases, and possible treatments.




A list of many marine fish diseases, and possible remedies to help cure the sick.




An in-depth study of many of the popular medicines on the market today.




A  hands-on approach to diagnosis, feeding, and treatment.

Freshwater Diseases

Saltwater Diseases


Treatment and Methodology

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