Meeting Abstract
Two prominent model fishes, zebrafish and guppies, produce tiny offspring (3.5-5.5 mm in length), yet guppies spend nearly an order of magnitude more time developing in utero prior to first feeding. Suction feeding at small size is thought to be constrained by the hydrodynamics of actuating small mouthparts quickly through a viscous medium. By manipulating water viscosity, we control the hydrodynamic regime (measured as Reynolds number, Re) to ask what effect developmental time has on offspring maturation, feeding performance and suction generation between these two species. Ossification rate is used as a measure of morphological maturation and was found to be similar between the two species: each species is 50% ossified at 7.25 mm in length. Despite that first feeding occurs prior to each species reaching even 10% maturity, capture success of suspended prey is significantly higher in guppies (90% vs. 20%). As Re increases, both species are able to capture prey at increasing distances, but at any given Re, guppies successfully feed at greater distances to prey. Both offspring generate negative pressures during a strike, but suction is simultaneously associated with ram feeding. Particle imaging shows that a bow wave leads the approaching zebrafish larvae, which pushes the prey item ahead of the mouth by 0.5 head length. During the suction event, the bow wave temporarily ceases, and the momentum of the larvae allows it to capture the stationary prey. An approaching guppy offspring also produces a bow wave, but due to greater oral jaw protrusion and lateral head expansion, the suction field generated by the guppy extends beyond the horizon of the bow wave. A larger suction field might allow guppy offspring to feed at greater distances and with higher success rates, but maturation of the skeletal system alone does not explain this observation.
