Meeting Abstract
Derived bony fishes have a spiny portion of the dorsal fin which has been proposed to have either a defense or stability function. We used bluegill sunfish to investigate how this structure functions during steady swimming at 1BL.s-1 in the presence or absence of turbulence. We collected kinematic data with the fin intact (injection of saline) and after the injection of flaxedil – a muscle relaxant – or lidocaine – an afferent nerve blocker. We hypothesize that there will be no differences during steady swimming with the sensory nerves blocked or with the muscle function impaired by flaxedil. However, when exposed to turbulence, we expect the fish to lose its heading more often when deprived of the sensory information and even more frequently when the muscle relaxant is applied. Flaxedil, lidocaine, and Ringer’s saline solutions were injected at three points on either side of the base of the spiny dorsal fin. Fish were allowed to recover in a flow tank and made to swim at 1BL.s-1 in quasi-laminar and turbulent flows while collecting high speed video. Turbulence was generated upstream from the fish with two rotating turbines. In control conditions (saline injection), the spiny dorsal fin is normally collapsed with no turbulence, but becomes erected in the presence of turbulence to aid in recovery from spills. Fish injected with flaxedil are unable to raise their spiny dorsal fin as expected. Fish injected with lidocaine also fail to deploy the spiny dorsal fin in response to perturbations. When exposed to turbulent conditions, fish injected with lidocaine and flaxedil increased spill rate and have decreased stability. These results support our hypothesis of a stabilizing role of the spiny dorsal fin under unsteady flows.
