INFLUENCE OF LARVAL GIZZARD SHAD (DOROSOMA-CEPEDIANUM) DENSITY ON PISCIVORY AND GROWTH OF YOUNG-OF-YEAR SAUGEYE (STIZOSTEDION-VITREUM X S-CANADENSE)

Growth and survival of young-of-year saugeye (Stizostedion vitreum female x S. canadense male) (stocked into Ohio reservoirs to create sport fisheries) are probably influenced by prey availability, Variations in which may account for historically documented variability in stocking success. Because saugeye switch from a diet of zooplankton to fish once stocked, we sought to determine experimentally if saugeye size and available ichthyoplankton, i.e., larval gizzard shad (Dorosoma cepedianum), affected this switch and whether piscivory improved saugeye growth. In an enclosure experiment, saugeye (33.9 mm TL) immediately switched to piscivory when exposed to ichthyoplankton densities of 20 and 100.m(-3), growing faster when more gizzard shad were available. In another enclosure experiment, saugeye 30-49 mm TL consumed 14-mm gizzard shad. In ponds (N = 4 ponds treatment(-1)) containing zooplankton and chironomids, we compared saugeye growth with and without larval gizzard shad and found, as in the first enclosure experiment, that piscivory improved saugeye growth. Neither saugeye size nor ichthyoplankton density influenced how quickly saugeye switched to piscivory. We conclude that managers should stock saugeye greater than or equal to 30 mm 1-2 wk before peak ichthyoplankton densities to improve saugeye growth and survival by enhancing opportunities for exploitation of young-of-year gizzard shad.