Ontogeny of routine swimming speed and startle responses in red drum, with a comparison of responses to acoustic and visual stimuli

Abstract

Routine swimming speed of larval red drum Sciaenops ocellatus increased throughout development but most rapidly for larvae >10 mm LT. Red drum of all sizes swam faster than predicted by published summary equations based on other species, possibly due to more advanced development at a given length. Frequency and magnitude of startle responses increased over the larval period for both types of stimuli with most of the improvement taking place before larvae reached 8 mm LT. Time to response for an acoustic and visual stimulus decreased early in the larval period but levelled off after 10 mm LT. Response distance and response speed for both stimuli generally increased throughout the larval period, but response duration remained constant. Visually stimulated responses were generally longer in duration and distance covered than acoustically stimulated responses, while mean response speeds were similar.