Pw. Webb et D. Weihs, HYDROSTATIC STABILITY OF FISH WITH SWIM BLADDERS - NOT ALL FISH ARE UNSTABLE, Canadian journal of zoology, 72(6), 1994, pp. 1149-1154
The center of mass and the center of buoyancy were found to occur at t
he same relative longitudinal location along the body of the elongate-
bodied European eel (Anguilla anguilla), the fusiform yellow perch (Pe
rca flavescens), and two gibbose species, rock bass (Ambloplites rupes
tris) and bluegill (Lepomis macrochirus). The locations of these cente
rs were not affected by fish size. Therefore the fish were neutral in
hydrostatic pitching equilibrium. The vertical location of the centers
of mass and buoyancy were the same for bluegill, but the center of ma
ss was dorsal to the center of buoyancy in yellow perch. The observati
ons on bluegill show that neutral hydrostatic rolling equilibrium is p
ossible. Our conclusions on similarity or separation between the locat
ions of the centers of mass and buoyancy derive from tests of signific
ance and differ from conclusions reported elsewhere on the basis of me
an Values only. In general, fish with swim bladders can be at or close
to neutral hydrostatic equilibrium but any disturbance will be destab
ilizing. This probably explains continuous fin-beating of fish in appa
rently still water.