EVALUATION OF STOCKING DENITY AND FEED REGIMES DURING EARLY LARVAL CULTURE OF SOUTHERN FLOUNDER Paralichthys lethostigma

Southern Flounder (Paralichthys lethostigma) are distributed throughout inshore waters along the Southeastern Atlantic and Gulf of Mexico coastline. They have been heavily targeted by fishermen in recent years which has led to severe population declines. This has prompted more stringent management regulations and stock enhancement programs in multiple states. The South Carolina Department of Natural Resources initiated a stock enhancement program for the species in 2021 and has been heavily focused on applied research to improve production. Focus has been on all production stages, but larval culture is of the highest priority to maximize production while ensuring proper pigmentation and an equal sex ratio of individuals produced.

From January through March of 2025, staff at the Waddell Mariculture Center and Marine Resources Research Institute completed multiple larval culture trials focused on stocking density or feeding regimes during the early stages of larval culture. All trials utilized 2-day post hatch larvae that were stocked into replicated (n ≥ 4) 18-L black wall cylindrical tanks and cultured under experimental conditions for 13-17 days. Stocking densities of larvae tested were 25, 50, 100, and 150 larvae/L. Feeding regimes tested included once daily feedings of either 10, 20, or 30 rotifers/mL or three times a day feeding where larvae were fed 10 rotifers/mL at first light followed by two subsequent feedings of 5 rotifers/mL four hours apart. Output parameters monitored included final survival and growth, and GLMM with a binomial distribution and ANOVA followed by Tukey’s post hoc test used for analysis of those parameters, respectively.

Results suggest that early larval output of southern flounder can be improved by stocking at a high density of 150 larvae/L (Figure 1) and by a feeding regime of 10+5+5 rotifers/mL at 4-hour intervals.