Meeting Abstract

137.2  Monday, Jan. 7  The crucial effect of hydrodynamics on feeding efficiency during the “critical period” of fish larvae. CHINA, V*; HOLZMAN, R; Tel Aviv University; The Interuniversity Institute for Marine Sciences in Eilat victor.china@gmail.com

Survival of the larval stage of marine fishes has far-reaching consequences in determining their rates of settlement, population size and stability. While feeding performance is known to play a central role in determining survival, there is little information on the mechanisms of prey capture by fish larvae. The hydrodynamic forces that govern suction feeding performance are expected to change through the larvae’s ontogeny, as the larvae transition from a viscous-dominated regime to a realm of higher Reynolds numbers. We used numerical simulations, feeding experiments and hi-speed video observations to test the direct effect of viscosity on larval feeding performance. Computational fluid dynamic (CFD) simulations revealed that the flow generated at small mouth sizes is characterized by shallow spatial gradients compared to that measured for high Reynolds numbers. Prey-capture rates were positively correlated with larval size and negatively correlated with viscosity; primarily due to mechanistic effects of the suction flow and reduced capture success. High-speed photography indicated that in order to feed successfully under conditions of increasing viscosity, the larvae had to open their mouths faster and wider. Starvation is considered a primary cause of mortality in the early stages of larval fishes, as suggested a decade ago in Hjort’s “critical period” hypothesis. Our findings indicate severe hydrodynamic constraints on the efficiency of suction-feeding at the size range typically associated with that “critical period”. These constraints could explain starvation and low survival of larval fish and also imply an evolutionary constraint on the minimal larval size at hatching.