Prey size selection and growth dynamics of American shad larvae

Widespread declines in stocks of American shad Alosa sapidissima have been attributed to overfishing, decrease in water quality, and loss of habitat.  Recent surveys in North Carolina suggest that stocks are continuing to decline despite management and stock enhancement.  Laboratory experiments were conducted to evaluate the effect of prey density on growth and survival of American shad.  Larvae were reared from 12 to 20-d posthatch in five treatments: (1) no food; (2) low-zooplankton, which simulated prey densities in Roanoke River; (3) medium-zooplankton, which simulated prey densities typical of coastal watersheds; (4) high-zooplankton, and (5) Artemia nauplii.  Larval survival was 35 ± 7% and was not significantly different among treatments.  Highest survival was observed with fish fed high concentrations of zooplankton (46 ± 18%) followed by Artemia (40 ± 16%).  Length-specific growth rates were 0.039 for Artemia, 0.034 for high-prey, 0.029 for medium-prey, 0.024 for low-prey, and 0.017 for starved treatments.  Larval growth as a function of length was not significantly different between Artemia and high-zooplankton; however, these treatments were significantly higher than the lower prey densities (ANOVA; P < 0.0001).  Results suggest that zooplankton densities common to Roanoke River and Albemarle Sound are not optimal for growth of American shad.