Meeting Abstract
Larval fish suffer prodigious mortality rates during the transition from feeding on their yolk sac to actively capturing prey. This mortality has broad implications for population structure and ecology of fishes, and understanding the mechanisms that affect their survival and growth has been an ongoing effort in fish biology. To actively capture prey, larval fishes rapidly open their mouth to generate a flow of water external to the mouth. This “suction flow” is key to feeding success, because it draws the prey item into the predator’s mouth, countering any escape response of the prey. However, because larval fish are minute, they start feeding in a low Reynolds numbers (Re) regime, and the hydrodynamics of their suction flows is different than that of their older conspecifics. Coincidently, feeding and capture success rates are low at first feeding, but increases rapidly with ontogeny. In this review, we will describe the biomechanics and hydrodynamics of suction feeding in low Re. We will outline why this hydrodynamic regime impedes suction feeding performance, reducing feeding success and feeding rate, ultimately resulting in “hydrodynamic starvation” in first feeding larvae. Hydrodynamic modelling and high-speed videos show that, for suction feeding in low Re, spatial-temporal gradients are weak, resulting in a diminished ability to exert strong acceleration-bases forces on the prey. In addition, flows inside the mouth cavity facilitate rejection and ejection of prey items after these already crossed the gape into the mouth. Dynamic scaling experiments indicate that these failures result from the hydrodynamic regime imposed on the larvae, directly related to their size. Other age-related changes in morphology, cognition and coordination have relatively small effects on feeding rates and capture success in first feeding larvae.
