The swim bladder is an internal organ that helps fish maintain their buoyancy and control their depth in the water. It is a gas-filled sac located near the spine and is connected to the digestive tract. By adjusting the amount of gas in the bladder, fish can rise or sink in the water.
Black moor goldfish have a single-chambered swim bladder, which means it has one large compartment rather than multiple chambers. This type of swim bladder is common among goldfish and other carp species.