COMPARISONS OF LARVAL WALLEYE AND SAUGEYE (WALLEYE X SAUGER HYBRID) GROWTH AND IMPACTS ON ZOOPLANKTON IN EXPERIMENTAL PONDS

We studied growth differences of larval walleye (Stizostedion vitreum) and saugeye (the hybrid of female walleye and male sauger S. canadens e) by monitoring their growth and consumption in hatchery ponds stocke d at different densities (10 or 50 fish/m3) and studying concurrent zo oplankton dynamics. Walleyes pined more weight than saugeyes, but grow th of both walleyes and saugeyes was inversely related to stocking den sity. At harvest, mean weights of walleyes and saugeyes were 0.67 and 0.57 g for those reared at low density, and 0.32 and 0.23 g for those reared at high density. Stomach content analysis showed that both fish species selectively fed on Daphnia and Cyclops, and also selected for Bosmina when large zooplankton species were less available. In ponds, the biomasses of Daphnia, Cyclops, Diaptomus, and nauplii were greate r in ponds where fish density was low than in ponds where fish density was high, but did not differ between fish species stocked. Impacts of fish on zooplankton biomass depend on fish density rather than fish s pecies. We suggest that walleye and saugeye can be managed similarly i n hatchery ponds.