Goldfish are able to swim because they have sleek, symmetrical bodies. A bloated fish may have trouble swimming, and may be suffering from illness or infection. Seek qualified advice if you are concerned about the health of your goldfish.
Constipation can cause a fish to appear visibly bloated. In particular, fancy types of goldfish commonly have problems with constipation, due to the unusual shapes of their bodies. A constipated goldfish will become bloated, be unable to defecate and may have problems swimming normally. If your fish is constipated, you can help by feeding cooked peas with the skin removed. Fish that are prone to constipation should be fed peas on a regular basis.
If the water temperature is correct for breeding, and male fish are present, female goldfish will lay eggs as part of the breeding process. Before laying eggs, a female goldfish may become bloated as her body fills with ova. If you want to control the spawning of your goldfish, keep male and female fish separately. Female goldfish can be artificially induced to release their eggs if spontaneous spawning is not going to be allowed in your aquarium or pond.
Like humans, goldfish can become obese if the number of calories they take in regularly exceeds the number of calories they burn through exercise and basic metabolic function. It is unusual for goldfish to significantly overeat, so you should avoid overfeeding your fish as a safeguard against obesity. Feed your fish little and often, and follow the directions on your goldfish food packaging regarding appropriate feed quantities per fish.
Illness and Infection
Sadly, a bloated goldfish may be suffering from a serious physical illness, infection or even a tumor. If the internal organs of a goldfish are infected or malfunctioning, this can lead to bloating. A condition known as dropsy causes goldfish to become bloated -- additionally their scales will become raised and their body coloration may lessen. Dropsy occurs as a result of malnutrition or infection -- commercial medications are available to treat dropsy. Additionally, you can improve the chances of survival for your goldfish by changing one quarter of the aquarium water every other day.
Jae Allen has been a writer since 1999, with articles published in "The Hub," "Innocent Words" and "Rhythm." She has worked as a medical writer, paralegal, veterinary assistant, stage manager, session musician, ghostwriter and university professor. Allen specializes in travel, health/fitness, animals and other topics.