February 15-18, 2009 Washington State Convention Center Seattle ...

EFFECT OF ZOOPLANKTON DENSITY ON GROWTH OF LARVAL AMERICAN SHAD
Alosa sapidissima: AN EXPERIMENTAL APPROACH
Kenneth L. Riley, Samantha M. Binion, Travis T. Williams and Anthony S. Overton
East Carolina University
Department of Biology
Greenville, North Carolina 27858 USA
klr1011@ecu.edu
Widespread declines in stocks of American shad Alosa sapidissima along the Atlantic Coast 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 extensive management and stock enhancement efforts. We hypothesize that the precipitous decline in American shad
reflects the availability of suitable nursery habitat and food resources for early life stages in Roanoke River and Albemarle
Sound. The goal of this study was to conduct laboratory trials to evaluate the effect of prey density on growth and survival of
American shad. Larvae were reared at 25 C from 12 to 20-d posthatch in five treatments: (1) starvation; (2) low-prey, which
simulated natural prey densities in Roanoke River; (3) medium-prey, which simulated natural prey densities in adjacent riverine
systems; (4) high-prey, and (5) Artemia nauplii. The latter treatments simulated prey densities typically used in hatchery
operations. Wild zooplankton collected from local waters were used as prey. Zooplankton were identified and measured. Zooplankton
primarily consisted of cladocerans (29%), copepod nauplii (25%), rotifers (24%), and copepod adults (19%). Larval
survival was 35 ± 7% and was not significantly different among treatments. The highest survival was observed with fish fed
high concentrations of prey (46 ± 18%) followed by Artemia (40 ± 16%). The lowest survival was observed with starved fish
(22 ± 12%). Length-specific growth rates (G l ) determined from total length measurements were 0.069 for Artemia, 0.056 for
high-prey, 0.029 for medium-prey, 0.017 for low-prey, and 0.009 for starved treatments. Larval growth as a function of length
was not significantly different between Artemia and high-prey; however, these treatments were significantly higher than the
lower prey densities (ANOVA; P < 0.0001). Weight-specific growth rates (G w ) determined from dry weight measurements
were significantly higher for Artemia (G w = 0.851; P < 0.0001) and remained relatively low for all other treatments (G w =
0.617). Evidence from this research shows that zooplankton densities common to Roanoke River and Albemarle Sound are
not optimal for growth of American shad. Releases of hatchery-reared fish should be timed to coincide with natural peaks in
zooplankton production.
FIGURE 1. Growth (mean
± S.E.) of American shad
larvae reared at 25 C and
cultured in 12-L tanks (3
fish L -1 ). Prey densities
ranged from 1.0 x 10 3 to
1.0 x 10 6 individuals m -3 .
2 3