Influence of stocking density on growth and survival of intensively reared Walleye fry during larval culture

ABSTRACT Objective The objective of this study was to investigate the impact of stocking density on the early growth performance and survival of intensively reared Walleye Sander vitreus by stocking fry at different densities in a replicated, flow-through larviculture system. Methods Three stocking densities were evaluated (low: 6.25 fry/L; medium: 12.5 fry/L; high: 18.75 fry/L) in triplicate in a larviculture system with 240-L tanks and clay suspension. Tanks were cleaned and siphoned daily to remove and count dead fish for daily observed mortality. At 10-d intervals, 25 fish/tank were lethally sampled for total length and weight measurements. Observations of gut fullness, swim bladder inflation, and deformity rate were also recorded. Results Walleye fry in the low-density treatment had significantly greater growth than those in the medium- and high-density treatments. Fry in the medium-density treatment also outperformed the high-density treatment. Survival rates were significantly influenced by density treatment. The medium-density treatment had significantly higher percent survival than the low- and high-density treatments, but survival was similar between the low- and high-density treatments. There were no significant differences in total yield (total number of surviving fish) between the high- and medium-density treatments; however, the low-density treatment yielded significantly fewer surviving fish than the other treatments. Conclusions Consideration is needed with regard to stocking density for Walleye fry, as no one stocking density outperforms the others in all metrics. If the goal is to produce many Walleye, the medium density (12.5 fry/L) should be considered. However, if the goal is to produce the largest Walleye, the low-density (6.25-fry/L) treatment provided the best growth performance. These results can guide producers when selecting the optimal densities to achieve the goals of their operation.