Early Life History of Fishes in the San Francisco Estuary and Watershed

The Effect of Light Intensity, Alga Concentration, and Prey Density on the Feeding Behavior of Delta Smelt larvae

Bradd Baskerville-Bridges, Joan C. Lindberg, and Serge I. Doroshov

doi: https://doi.org/10.47886/9781888569599.ch14

Abstract.—Understanding how environmental factors influence first feeding success is critical for the conservation-oriented larval culture of delta smelt Hypomesus transpacificus, a threatened osmerid endemic to the San Francisco Estuary. We investigated the effects of light intensity, alga concentration, and prey (rotifer) density on feeding of cultured delta smelt larvae. In one experiment, first feeding larvae were exposed to three light intensities (0.01, 0.3, and 1.9 μmoles ^. s^–1. m^–2) and three alga concentrations (0, 0.5, and 2 × 10⁶ cells/mL). Intestinal contents were examined to determine the incidence of feeding and gut fillness. Maximum feeding responses (92% feeding; 4.8 rotifers/feeding larva in 2 h) were observed at the highest light intensity and alga concentrations; feeding sharply declined with a reduction of either factor. A second experiment was performed to study the effect of alga concentration (0, 1.5, 3, and 6 × 10⁶ cells/mL) in more detail. Feeding responses were very low without algae (13% feeding; 2.1 rotifers/feeding larva in 2 h), but dramatically increased at high concentrations (83% feeding; 5.1 rotifers/feeding larvae in 2 h). In a third experiment, the effect of prey (rotifer) density (0.1, 1, 10, and 100 rotifers/mL) was tested, which significantly enhanced feeding up to the 10/mL treatment (84% feeding; 4.2 rotifers/feeding larvae in 1 h). All three environmental factors significantly affected feeding success of larval delta smelt. Optimization of these factors has improved survival and growth during the sensitive larval period and has improved laboratory culture of delta smelt.