What organ controls the buoyancy of bony fish?

The swim bladder is a gas-filled organ located in the body of bony fish that plays a crucial role in controlling buoyancy. This organ allows fish to maintain their position in the water column without expending excessive energy. By adjusting the volume of gas within the swim bladder, fish can ascend or descend in the water. When the bladder is filled with gas, the fish becomes lighter and can rise, while releasing gas will make the fish heavier and cause it to sink.

In contrast, the other options do not fulfill the function of buoyancy control. The stomach is primarily involved in digestion rather than buoyancy. The heart is responsible for pumping blood throughout the body and does not have a role in buoyancy regulation. The anterior kidney, while important for excretion and osmoregulation, is not involved in buoyancy control in fish. The function of buoyancy regulation is specifically and effectively managed by the swim bladder, making it the correct answer.