Meeting Abstract

89.3  Thursday, Jan. 7  The mechanics of ventilation in a scombrid fish STROTHER, J.A.*; WEGNER, N.C.; GRAHAM, J.B.; Univ. of California, Irvine; Scripps Institution of Oceanography; Scripps Institution of Oceanography strother@uci.edu

Many scombrid fishes are capable of achieving remarkably fast swimming speeds, which they are often able to maintain during long distance migrations. The elevated metabolic rate required for such activity is believed to be supported by a number of specializations in the gill morphology of these species. Increases in the respiratory surface area and decreases in the diffusional barrier thickness result in elevated diffusion capacities. Simultaneously, fusions that join adjacent filaments or secondary lamellae are thought to reinforce the gills to prevent deflection in the ventilatory flow stream. To examine the functional consequences of these differences in gill morphology, the flow around the gills of a scombrid fish was measured using particle image velocity (PIV) and the bending stiffness of the gills was measured using three-point bending. The freshly-excised gill arches of a bonito (Sarda chiliensis) were placed in a closely fitting flow-through chamber, and the flow rate through the chamber was varied. PIV was used to measure the velocity of water along the trailing edge of the primary lamellae, from which several measures of respiratory efficiency were calculated. The bending stiffness of the gills was measured using a modified three-point bending fixture, with the deflection parallel to the ventilatory flow and the bending moment parallel to the gill arch. We found that, with the observed flow rates, non-respiratory shunting and flow heterogeneity remained low. However, as the flow rates increased these effects began to compromise respiratory performance. It is possible that such effects impose functional constraints on the rate of ventilation and the morphology of the gills in scombrid fishes.