An action spectrum for the light-dependent inhibition of swimming behavior in newly hatched white sturgeon, Acipenser transmontanus

Newly hatched white sturgeon (Acipenser transmontanus) yolk-sac larvae are negatively phototactic, photokinetic and geotactic--seeking cover in the substrate during daylight hours. If cover is unavailable and the light intensity is low, they move into the water column and alternate periods of rapid, upward swimming with periods of quiescence during which they sink. In the dark they swim almost continuously. A flash of light inhibits swimming activity totally for a period dependent on the light intensity. Using this observation, we obtained an action spectrum for swimming inhibition for 30 newly hatched larvae. This action spectrum is best fit by a single visual pigment with absorbance maximum at 537 nm. The lack of red sensitivity fits well with previous work showing that red-sensitive photoreceptor cells are absent in young sturgeon. The possible significance of red insensitivity is discussed from both ecological and practical standpoints.