EIDIETIS, L.*; WEBB, P.W.; FORRESTER, T.L.: The abilities of two morphologically different fishes to counteract rolling disturbances

We increased rolling moments and decreased negative metacentric heights of spiny rayed Lepomis macrochirus (bluegill) and soft rayed Semotilus atromaculotus (creek chub) by attaching weights and floats which, together, were neutrally buoyant. Weight and buoyant force were normalized by fish mass, and moment arms and metacentric heights by volume^-1/3. Fish behavioral responses used to counteract the disturbance were observed in conditions that restricted swimming and in conditions that allowed free swimming. Threshold responses were defined when a disturbance first caused fish to roll 90^� (the limit of initial stability) and when fish were not able to right themselves (the limit of ultimate stability). When swimming was restricted, initial stability was greater for chub than bluegill. When conditions allowed free swimming, initial stability was similar for both species. Ultimate stability was similar for both species irrespective of whether swimming was restricted.