Factors affecting first-year survival of stocked walleyes and methods for intensive culture of walleye fry

Pennsylvania hatcheries annually produce nearly 100 million walleyes (Stizostedion vitreum) for stocking of inland lakes and reservoirs. Because fry can be produced in greater numbers and at less expense than fingerlings, the vast majority of walleyes reared in Pennsylvania are stocked as fry. The first objective of this study was to evaluate several pre-stocking variables that may affect short term survival of walleye fry. In a 24-h simulated stocking bioassay, I evaluated survival of hatchery-reared walleye fry subjected to several different production variables. Fry survival ranged from 80% to 96% among all treatment groups, indicating that high poststocking mortality is not a result of production variables within the ranges tested.; The second objective of this study was to quantify and evaluate the relative importance of these two variables. Over a 2-year period, I measured spring zooplankton densities and predator abundance in relation to fry survival in five reservoirs located in western Pennsylvania. When peak zooplankton densities were less than 100/L, few walleye fry survived until fall. Fry survival was highest when densities of daphnids and copepods exceeded 100/L and densities of potential fry predators were low. These findings indicate that food availability and predator abundance may impose sequential limitations on first-year survival of stocked walleyes.; Although stocked walleye fingerlings exhibit much higher survival than fry, the expense and space requirements of current production methods have limited fingerling production at most hatcheries. The third objective of this study was to test the feasibility of intensively rearing walleye fry on brine shrimp at production levels using culture densities 2-3 fold greater than those in current use. After 23-d of intensive culture, the system produced more than 333,000 advanced fry (17-18 mm) from initial densities of 40 and 60 fry/L. Growth of fry was slightly higher (4.5%) at 40 fry/L than at 60 fry/L, but yield was substantially higher (37.8%) at 60 fry/L. Survival was not significantly different between densities. These findings demonstrate the feasibility of intensively rearing walleye fry on brine shrimp at production levels.