Response latencies to postural disturbances in three species of teleostean fishes.

Flow in aquatic systems is characterized by unsteadiness that creates destabilizing perturbations. Appropriate correction responses depend on response latency. The time between a disturbance induced by either removal of a flow refuge or striking various parts of the body with a narrow water jet was measured for three species, chosen as examples of modes in teleostean body/fin organization that are expected to affect stability. Creek chub Semotilus atromaculatus is representative of fusiform-bodied soft-rayed teleosts, smallmouth bass Micropterus dolomieu of fusiform-bodied spiny-rayed forms and bluegill Lepomis macrochirus of deep-bodied spiny-rayed forms. Observations were made at 23 degrees C. Loss of refuge resulted in a surge that fish corrected by starting to swim within 129+/-29 ms (mean +/- 2 S.E.M.) for chub, which was significantly shorter than minimal times of approximately 200 ms for bluegill and bass. Slips and heaves induced by water jets initially resulted in extension of the median and paired fins that would damp growth of the disturbance, but otherwise these disturbances were ignored. Yaws and pitches were more likely to cause fish to swim away from the stimulus, making corrections as they did so. There were no differences in latencies for slip, heave, yaw and pitch disturbances within each species, but latencies varied among species. For these disturbances, responses averaged 123+/-19 ms for chub, again significantly smaller than those of 201+/-24 ms for bass and 208+/-52 ms for bluegill. Values for the two centrarchids were not significantly different (P>0.08). The response latency for rolling disturbances did not differ among species but was significantly smaller than that for other disturbances, with an overall latency of 70+/-15 ms. The greater responsiveness to hydrostatic rolling instability is attributed to functions requiring an upright posture and differences among species in habitat preferences.