Goldfish tend to eat constantly. Fish who are fed too much will eat whatever they are given, and eventually this results in constipated goldfish. For a goldfish, this is a dangerous condition that should be taken very seriously. Some types of goldfish have more trouble with this than others do. Fancy goldfish, for example, are prone to digestive issues due to their egg-shaped bodies, which means the internal organs take on abnormal shapes as well.
Swelling of Fish's Body
A constipated goldfish will look fatter than usual, with little warning, and this has nothing to do with the breeding season when the females naturally grow heavy with roe. This symptom may be difficult to discern, especially in fish that are naturally egg-shaped, such as the fancy ryukins, orandas, ranchus and black moors. The aquarist who is familiar with the natural shape of the fish will recognize any sudden changes in the fish's appearance.
Some fish with constipation will swim sluggishly, perhaps slowly following other fish around the tank, or hanging around on the bottom as if sick or dying. Any fish exhibiting these symptoms is not feeling well and doesn't have his typical energy level. This is easy to determine if the affected fish is normally quite active, which most healthy goldfish are. While some fancy goldfish naturally swim slowly, the comets and common goldfish are rapid swimmers.
This symptom is usually the aquarist's first indication that something is wrong with a fish, regardless of the actual condition. A healthy fish will have a wide spread tail and fins, and a proud dorsal, but a sick fish will clamp his fins tightly and droop his tail. The sick fish also will tightly clamp his dorsal fin to his back.
Lack of Fish Waste
Constipated fish don't defecate satisfactorily, which is caused by the fish being fed an improper diet or getting fed too much, too fast. The bowel blocks up with rotting food and the fish is unable to pass the blockage. The bowel then swells and the fish is highly stressed and in pain. The cure for this is to sprinkle a little aquarium salt in the tank as a laxative and fast the fish for five days.
Air Bladder Disease
When fish are constipated they quite often develop problems with their air bladders, which is the organ that keeps fish swimming upright. This condition is identified when the fish is unable to remain upright for long. He may float upside-down or nose down, or swim on his side. These are all classic symptoms of air bladder disease and are treated with aquarium salt as a laxative and five days of fasting for the affected fish.