Peas are extremely important for the digestive system of goldfish. Peas are very high in fiber, so they prevent constipation, which is often referred to as swim bladder disease in goldfish. Many people do not understand that commercial goldfish flakes and pellets do not have enough fiber in them to sustain a healthy digestive system. Not only is swim bladder disease uncomfortable for your fish, untreated it can become fatal. Do to lack of fiber, the digestive system will fill with gas from constipation, and the goldfish will be unable to swim. With no control over their movements any longer, they generally either sink to the bottom of the aquarium or float to the top unable to go back down. I greatly urge you to feed your fish at least one pea a week to prevent this from happening, but if it does happen immediately start to feed the fish nothing but peas until the fish is back to normal. In the case of the fish sitting on the bottom of tank and not floating on the top, it could be a bacterial or parasitic infection causing the fish to be too weak to swim, so always check to make sure your fish does not have signs of infection daily because the fish will need antibiotics or ant parasitic medications to save it. Always, also inspect the fish’s feces for air bubbles daily, as air bubbles in the feces is also a sign of too much air in the swim bladder. I suggest feeding the fish the approximately the same amount of peas as you would feed pellets or flakes that day to cure swim bladder disease, so if you feed six medium size pellets a day, you would feed about three peas a day since peas are generally twice the size of a pellet. When feeding frozen peas, defrost peas first, then shell and slice in half or fourths so small goldfish can consume them easily.
So maybe you are thinking as you read this “peas don’t naturally grow in goldfishes’ habitat.” In their natural habitat they graze on aquatic plant life and even algae. You can find these plants at certain pet shops to add to your aquarium, but keep in mind they may not live long with a school of hungry goldfish around. If they do survive there is a lot of upkeep to consider before adding them to your aquarium, like removing any dying leaves since they will cause nitrate levels to increase in the aquarium. They also need adequate lighting and chemicals to fertilize them. Even if you decide to grow aquatic plants, keep feeding peas since they are so fibrous.
There are also other fruits and vegetables that your goldfish might enjoy as a treat such as small orange segments without the casing, small pieces of melon, zucchini, squash, and carrot, with moderation since goldfish can not comprehend when to stop eating on their own. Any green leafy vegetable such as endive, escarole, and romaine lettuce are also a healthy snack. So remember variety is the spice of life even when it comes to a goldfish’s diet.