Effects of light and turbidity on feeding, growth, and survival of larval Delta Smelt (Hypomesus transpacificus, Actinopterygii, Osmeridae)

Understanding how environmental factors—here, light intensity and turbidity—influence the feeding, growth, and survival of larval Delta Smelt is critical for optimizing the culture of this endangered fish species. Three sets of rearing trials were conducted where larvae were cultured under different levels of turbidity and light intensity. Delta Smelt larvae feeding activity was observed throughout the initial adjustment of light and turbidity levels to ascertain feeding ability and behavior at the different levels. It was found that there is a minimum threshold of combined light and turbidity to generate their exogenous feeding response. At low turbidity conditions, early-stage larvae begun feeding and growing earlier when light levels were higher. The condition factor and survival of the late-stage larvae was increased with increased turbidity. The results suggest Delta Smelt larvae may be cultured under lower turbidity and light conditions rather than at the currently used levels. We conclude that the interaction between turbidity and light intensity plays an important role in the feeding activity, growth, and survival of larvae. The results here may inform fish culture lab methodologies, but may also provide useful baseline knowledge for light and turbidity preferences of Delta Smelt larvae in the wild.