What primary function does a swim bladder serve in fish?

The swim bladder plays a crucial role in controlling buoyancy for fish, allowing them to maintain their position in the water column without expending energy. This gas-filled sac adjusts its volume based on the amount of gas it contains, which can be increased or decreased to help fish ascend or descend in the water. By regulating buoyancy, fish can conserve energy while navigating through their aquatic environment, making it easier to find food, evade predators, and reproduce. This adaptation is particularly important since different fish species inhabit various depths and conditions that require precise control over their buoyancy for survival.