Choosing Healthy Fish
Always select fish with bright eyes and a sturdy body. The fish should be lively, its large dorsal fins erect and its two ventral fins well expanded. A healthy fish will swim effortlessly, with its fins erect; it will also be able to remain perfectly still in the water.
Check that small fish in particular do not have damaged or missing scales, as the exposed tissue beneath the scales will be vulnerable to secondary fungal infection. Because larger fish are more aggressive, it is common for them to have some missing scales. If the spine of the fish appears to be bent, it could be the result of damage to the nervous system. A bloated body, bulging eyes and bristling scales are indicative of an unhealthy fish.