Relative abilities to correct rolling disturbances of three morphologically different fish

Abstract

Responses of three fish species were measured following the addition of neutrally buoyant weight-float combinations that increased rolling instability. The three species were creek chub, Semotilus atromaculatus, largemouth bass, Micropterus salmoides, and bluegill, Lepomis macrochirus. Ability to correct posture was predicted to increase with fin size and body depth in the order creek chub < largemouth bass < bluegill. In a 90-s period, the least added torque causing fish to roll to 90° in response to disturbances, ΔT90, and the least added torque making fish unable to recover from rolling, ΔTcrit, were measured as limits of ability to correct postural disturbances. Contrary to expectations, creek chub required a 58% increase in body torque to reach ΔT90, significantly larger than the 11% increase for largemouth bass and 19% increase for bluegill. Similarly, ΔTcritwas a 78% increase in body torque for creek chub, 43% for largemouth bass, and 34% for bluegill. Increased rolling torques resulted in behaviors reducing and avoiding rolling, including tilting, which reduces metacentric height, inverted swimming, which stabilizes fish, and contacting surfaces, which generates static forces. The superior ability of creek chub to correct postural disturbances may be explained by a fin arrangement that facilitates interactions with the ground.