Abstract
Suction feeding is thought to be the primary mode of prey capture in most larval fishes. Similar to adult suction feeders, larvae swim towards their prey while rapidly expanding their mouth cavity to generate an inward flow of water that draws the prey into the mouth. Although larvae are known to experience flows with lower Reynolds numbers than adults, it is unclear how the suction-induced flow field changes throughout ontogeny, and how such changes relate to prey capture performance. To address these questions, we determined mouth dimensions and opening speeds in Sparus aurata from first-feeding larvae to adults. We proceeded to develop a computational model of mouth expansion in order to analyze the scaling of suction flows under the observed parameters. Larval fish produced suction flows that were around two orders of magnitude slower than those of adults. Compared with adult fish, in which flow speed decays steeply with distance in front of the mouth, flow speed decayed more gradually in larval fish. This difference indicates that viscous forces in low Reynolds number flows modify the spatial distribution flow speed in front of the mouth. Consequently, simulated predator-prey encounters showed that larval fish could capture inert prey from a greater distance compared with adults. However, if prey attempted to escape then larval fish performed poorly: simulations inferred capture success in only weakly escaping prey immediately in front of the mouth. These ontogenetic changes in Reynolds number, suction-induced flow field and feeding performance could explain a widespread ontogenetic diet shift from passive prey at early life stages to evasive prey as larvae mature.
Highlights
The larval stage of most marine fish is spent in the pelagic environment, where they suffer very high mortality rates as a result of predation, advection away from favorable habitats and starvation (Cowen, 2002; Hunter, 1980; Leis and McCormick, 2002)
The time to peak gape ranged from 9 to 76ms (n=47 strikes) and was not correlated with fish standard length, mouth cavity length or peak gape diameter (Fig. 1A; linear regression; P>0.1; R2
On the basis of the observed scaling of mouth dimensions and mouth-opening speed in S. aurata, we developed a computational model of mouth expansion and evaluated the fluid flow patterns in front of the mouth at several life stages
Summary
The larval stage of most marine fish is spent in the pelagic environment, where they suffer very high mortality rates as a result of predation, advection away from favorable habitats and starvation (Cowen, 2002; Hunter, 1980; Leis and McCormick, 2002). The success rate of prey capture by larval fish rapidly increases with age (Houde and Schekter, 1980; Hunter, 1981). As larvae mature, their skeleton gradually ossifies, body and mouth grow and they experience a hydrodynamic regime. Received 24 February 2014; Accepted 20 August 2014 characterized by higher Reynolds numbers (Hernández, 2000; Houde and Schekter, 1980; Müller and van Leeuwen, 2004; Osse and van den Boogaart, 1999; Osse, 1989) These changes improve larval swimming and c-start performance, as well as detection of prey (Danos and Lauder, 2012; Müller et al, 2008; Müller and van Leeuwen, 2004; Müller and Videler, 1996; Osse and van den Boogaart, 1999). It has been hypothesized that the hydrodynamic regime experienced by small larvae reduces their encounter rates with prey or limits their ability to capture prey (Anto and Turingan, 2010; China and Holzman, 2014; Hernández, 2000; Houde and Schekter, 1980; Osse, 1989)
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