Meeting Abstract
Larval fishes experience extreme mortality rates, with 99% of a cohort perishing within days after they start to actively feed. While recent evidence suggests that hydrodynamic factors constrain larval feeding during early ontogeny, feeding in fish (and larvae) is a complex process that also involves numerous interacting behavioral and biomechanical components. How these components change throughout ontogeny and how they contribute to feeding success remain unclear. Using a dataset of over 300 feeding attempts, we quantified the effects of key morphological and behavioral traits on the feeding success of Sparus aurata during early ontogeny. Feeding success was determined using high-speed videography, under both natural and increased water viscosity treatments. We identified significant differences between successful and unsuccessful feeding attempts: Path analyses revealed that larval size affected feeding success both directly and indirectly, via its effect on mouth size and opening speed. Sparus larvae exhibited a behavioral response to the viscosity treatments, modifying their feeding kinematics by reducing ram speed and initiating feeding strikes from a closer distance to their prey. These modifications, while resulting in a relatively high success rate, compromised their overall feeding rate, suggesting an hitherto unrecognized trade-off between strike success and encounter rate. Our results also highlight the impeded feeding performance in a low Reynolds regime, mediated by larval size and inability to rapidly and broadly expand the mouth cavity at smaller size. We suggest that these performance impediments will mainly affect the ability of larvae to feed successfully on large evasive prey during early ontogeny.
