Meeting Abstract
The viscous fluid environment experienced by small, first-feeding fishes resists the ability to produce suction. Compounding the negative effects of small size is the observation that larval fish are inherently immature – first relying on exogenous food sources at as soon as 5 days post fertilization (dpf). Here we compare first-feeding performance, kinematics and hydrodynamics of two species of freshwater fishes (zebrafish and guppy) that produce offspring at 5 + 0.5 mm in length, but that undergo a 5-fold difference in developmental time (5 vs. 25 dpf, respectively). By manipulating water viscosity, we control the hydrodynamic regime, measured as Reynolds number (Re). Despite first-feeding occurring at similar levels of maturity for both species, capture success is significantly higher in guppies (90% vs. 20%). At any given Re, guppies successfully feed at five-times greater distances to prey (1.0 vs. 0.2 mm). Flow visualization reveals a bow wave is produced ahead of each approaching fish (zebrafish larvae ~ 0.2 mm; guppy offspring ~ 0.4 mm), limiting the predator’s proximity to prey. During suction, zebrafish larvae generate flow fields that extend up to, but not beyond, the bow wave. Guppy offspring, likely due to their capacity to protrude the oral jaws, generate a suction field that extends well beyond the horizon of the bow wave, thus leading to successful prey capture from much greater distances. We argue that the difference in observed suction performance, having experimentally controlled for issues of scale, can be best explained by the degree of maturation achieved at the time of first-feeding.
