The behavior, growth, and survival of witch flounder (Glyptocephalus cynoglossus) larvae in relation to prey availability: adaptations to an extendedlarval period

Foraging behavior and prey abundance are significant factors determining th e survival success of fish during the larval stage. Witch flounder (Glyptoc ephalus cynoglossus) are reported to have the longest pelagic stage of any northwest Atlantic flatfish. We used laboratory experiments to investigate the behavior and performance of witch larvae in relation to prey availabili ty during this important life history stage. In one experiment, larvae were reared at a range of prey densities (2000, 4000, and 8000 prey per liter) and their growth and survival were monitored for 12 weeks after hatching. I n a second experiment the foraging behavior of larvae was recorded during f eeding trials at a range of prey densities (250, 500, 1000, 2000, 4000, 800 0, and 16,000 prey per liter) during weeks 2-8 after hatching. The larval s earch strategy for prey appeared to change from one that was saltatory to o ne that was cruising, and the foraging behavior was not strongly affected b y variation in prey availability. The growth rate was rapid (0.53 mm-d) and was unaffected by changes in prey density as was survival. Witch flounder larvae likely have low prey requirements compared with yellowtail flounder and Atlantic cod reared under similar laboratory conditions The ability to forage effectively when prey is abundant or scarce and the low prey require ments of this species may be an adaptive response to the extended larval pe riod.