The Goldfish Sanctuary
Symptoms: Fish appears to be losing weight, head may appear too large for the body
It is first important to determine if your fish is feeding normally. Most often, goldfish are good eaters and are not too shy about eating. However, a more timid fish may be at a loss during feeding time, and so fish should be observed during feeding to make sure each gets a share of the food. In general, if a fish is rather smaller than his tankmates, he may not get as much food. If a fancy goldfish is kept with more common varieties, the fancy goldfish may be unable to acquire adequate food. Extra effort on the part of the keeper can often alleviate this trouble, with separation for the fish in question if necessary.
Wasting can also, however, be caused by tuberculosis. A tubercular fish usually feeds normally. For the sake of your other fish, it is important to determine if Tuberculosis is the cause.