The fish diseases are divided into two groups; Tropical and Coldwater. It is divided into two categories not because there is a distinction between them but because they apply more often to the class of fish under which they are listed. The suggested cures and symptoms apply to both classes. Obviously all nets, instruments, etc should be sterilized after use to prevent the spread of infection from the isolation tank.
White spot is the most common ailment, being simply a form of chill or fish influenza. When weakened by a sharp fall in water temperature the fish is unable to resist a tiny parasite that lodges on it, causing an irritation, a swelling visible as a tiny white spot the size of a pin point. These spots often appear first on the tail, next the fins and finally the body. If unchecked this disease will sweep through the tank as an epidemic.