Indigestion symptoms show when a fish swims in a listless or unbalanced manner. Excreta may hang from the anal pore for a length of time instead of breaking away and may be light colored or have gas bubbles interspersed in it.
Indigestion affects the air bladder that gives the goldfish buoyancy and balance. The air bladder opens into the digestive tract, so any gas produced from trying to digest poor quality food finds its way into the air bladder. It over-inflates the air bladder.
In extreme cases the goldfish will float upside down.
This condition affects the more rounded bodied goldfish varieties as their air bladders are more rounded in shape than in the slim bodied varieties.
If it isn’t caught quickly enough, the fish may become permanently imbalanced.
Stop feeding the fish immediately.
Move it to the sickbay and add non-iodized salt at two teaspoons per gallon.
Also add two teaspoons of Epsom salts per gallon to the water; it has the same effect as it does on humans.
If you have caught it in time, the fish will pass the food through its digestive system in a day or two and regain its balance.
Don’t feed the fish until it has regained its balance, even if it takes a week or more. It needs to clear the food and gas through its system and then deflate its air bladder to the correct level.
If after two weeks the fish is still imbalanced, feed it live or green food. Daphnia is an ideal food as it is a mild laxative but isn’t always available. If live food isn’t available, use frozen food and green vegetable matter.
After the fish is swimming normally, feed it only live or frozen food for a week before putting it back in its aquarium.
Throw out the food you have been feeding your goldfish, and include more live foods from now on.