Light-induced changes in the prey consumption and behavior of two juvenileplanktivorous fish

Walleye pollock and sablefish, as 0+ yr juveniles, are pelagic particulate feeding planktivores. We conducted a series of laboratory experiments to de termine how illumination influences prey consumption in these species, util izing live Artemia sp. as prey. Both juvenile walleye pollock and sablefish were characterized by a sigmoidal relationship between the log of illumina tion and the number of prey consumed, with greater prey consumption at high er illuminations. The threshold illumination below which fish were no longe r able to visually forage was approximately 5 x 10(-7) mu E s(-1) m(-2) for walleye pollock and 5 x 10(-5) mu E s(-1) m(-2) for sablefish, indicating that walleye pollock are better adapted for visual feeding at depth or at n ight than are sablefish. This is consistent with what is known about their vertical distributions at this Life stage; walleye pollock make daily verti cal migrations which keep them at lower illuminations than sablefish, which remain at or near the water surface throughout the diel cycle. Although fe eding more effectively in the light, both species were capable of detecting and capturing prey in darkness.