What structure allows fish to regulate their buoyancy in water?

What structure allows fish to regulate their buoyancy in water?

• A. Pharynx
• B. Gills
• C. Lateral line
• D. Swim bladder

Answer: (D)

The structure that lets fish control their depth in water is a gas-filled internal sac that can inflate or deflate to change the fish’s overall density. When this organ fills with gas, the fish becomes more buoyant and can rise or stay suspended with less effort; when it releases gas, the fish sinks. Gas is added to or removed from the sac through specialized mechanisms that vary among species, enabling depth adjustments without constant swimming. The other options are involved in respiration, sensation of the environment, or feeding, not in adjusting buoyancy, so they don’t serve this buoyancy-regulating function.

The structure that lets fish control their depth in water is a gas-filled internal sac that can inflate or deflate to change the fish’s overall density. When this organ fills with gas, the fish becomes more buoyant and can rise or stay suspended with less effort; when it releases gas, the fish sinks. Gas is added to or removed from the sac through specialized mechanisms that vary among species, enabling depth adjustments without constant swimming. The other options are involved in respiration, sensation of the environment, or feeding, not in adjusting buoyancy, so they don’t serve this buoyancy-regulating function.