Fig. 4. Measurement of the center of buoyancy of a parrot cichlid. (A) To find the desired straight line on which the center of buoyancy was located, a fish in an unconscious state was dropped into a simple test section. The test section (a rectangular, transparent water container) was narrow (width 9 cm), only slightly wider than the body of the parrot cichlid, so as to prevent the sinking fish from rolling and yawing and only allowing it to pitch. The sinking fish was filmed. (B) The straight line sought was simply determined on drawing a vertical line passing through the center of mass of a non-rotating fish body. This straight line (red) approximately connected the center of mass (CM) and the base of pelvic fin. CB, the center of buoyancy of the fish body, indicated by the blue filled circle.