Temperature effects on low-light vision in juvenile rockfish (genus Sebastes) and consequences for habitat utilization.

The absolute low-light sensitivity of four congeneric species of rockfish (genus Sebastes) was studied from analysis of electroretinograms measured in living fish. The purpose was: (1) to determine if temperature sensitive noise in rod photoreceptors affects the absolute limit to low-light sensitivity at environmentally realistic temperatures and light levels, and (2) to examine whether interspecific variations in habitat utilization within rockfish communities correlate with differences in visual sensitivity. It was found that the low-light sensitivity of individual retinae is inversely dependent on temperature, decreasing tenfold with a 10 degrees C increase in temperature. While in all four species, temperature had a similar effect on sensitivity, the absolute sensitivity levels were different. The four species could be divided into two groups based on measured sensitivity. Kelp and olive rockfish form a high-sensitivity group capable of responding to light levels approximately 50-fold lower than blue and black rockfish. The sensitivity groups correlated with reported diel activity patterns; the high-sensitivity group forages nocturnally, whereas members of the low-sensitivity group are quiescent during twilight and night and forage during the day.