Effect of light intensity and eye development on prey capture by larval striped bass Morone saxatilis
The efficacy of visual and non-visual feeding among pelagic striped bass Morone saxatilis larvae adapted to a turbid estuary was determined in the laboratory in clear water. Capture of Artemia salina (density 100 l−1) was significantly affected by the interaction between age of larvae (range: 8–25 days post-hatch, dph) and light intensity (range: 0–10·6 mol s−1 m−2 at the water surface). Visual feeding by larvae aged 9–11 dph was highest in dim light (0·086–0·79 mol s−1 m−2), with fish capturing up to 5 prey larva−1 h−1. As the larvae grew, prey capture in brighter light improved, associated with an increasing proportion of twin cone photoreceptors and improving ability of the retina to light- and dark-adapt. By age >22 dph, mean prey capture was greatest at highest light intensities (0·79 and 10·6 mol s−1 m−2) exceeding 100 prey larva−1 h−1. Incidence of feeding larvae generally improved as the larvae grew, reaching >80% in all light intensities from 16 dph onwards. The lower threshold for visual feeding, between 0·0084 and 0·03 mol s−1 m−2, remained constant as the larvae grew, despite an increasing density of rod photoreceptors. Below this threshold, non-visual feeding was evident at a low rate (<6 prey larva−1 h−1) that was independent of larval age.