EFFECTS OF LARVAL DENSITY ON THE GROWTH AND SURVIVAL OF WEAKFISH CYNOSCION REGALIS IN LARGE-VOLUME ENCLOSURES

We investigated the effects of 3 different stocking densities on growth and mortality of weakfish Cynoscion regalis larvae in large enclosures (1.4 m(3)) deployed in Delaware Bay, USA. Stocking densities were 50, 500 and 5000 larvae m(-3). Larvae in each treatment were fed natural zooplankton prey maintained at 250 prey items l(-1); this concentration of prey was based on values measured on the weakfish spawning grounds in Delaware Bay. We conducted separate experiments for early-stage (2 to 9 d post-hatching) and late-stage (9 to 17 d post-hatching) larvae. There was a significant effect of stocking density on growth regardless of larval age. Mean instantaneous growth rates (dry wt) ranged from 0.10 to 0.18 d(-1) for early-stage larvae and from 0.18 to 0.29 d(-1) for late-stage larvae. Instantaneous mortality rates were lower than reported field values for weakfish larvae, and there was no significant effect of stocking density. These results indicate that growth of larvae in densely populated patches may be diminished.