Mortality of First-Feeding Postlarval Walleye (Stizostedion vitreum) in Culture Ponds

Abstract

We examined mortality rates of postlarval walleye (Stizostedion vitreum) at the onset of exogenous feeding in extensive culture ponds. Food concentrations (≥49 zooplankters∙L−1) were apparently sufficient to support successful first feeding, and no critical period of starvation mortality was evident at this stage of life. The highest observed mortality rates were associated with interspecific or intraspecific predation pressure. At low predation pressure, mean survival from stocking to the 12-mm stage was 87% in 1988 and 90% in 1989, and instantaneous mortality rates were an order of magnitude lower than those reported for postlarval walleye in natural lakes. Mortality rates calculated over the early postlarval period (stocking to 12 mm; 9–11 d) were similar to those calculated over the entire culture period (88–107 d) when predation pressure was low. At low predation pressure and 49–159 zooplankters∙L−1, there was no significant relationship between postlarval mortality rates and zooplankton density. The condition of first-feeding postlarvae captured from the pond with the lowest mean zooplankton density (49∙L−1) was significantly higher than that of postlarvae deprived of food for 48 h. Starvation is probably not a major cause of postlarval morality when zooplankton densities are ≥50∙L−1.