The southern flounder (Paralicthys lethostigma) is a large commercially and recreationally important flatfish common in coastal waters of the southeastern US. Fisheries stocks show signs of decline across the Gulf of Mexico. Because of its fast growth rate, excellent flesh quality, euryhaline habits, and the limited and unpredictable availability from fisheries, this species has drawn interest from the aquaculture industry. However, southern flounder females reach much larger sizes than males, which reduces productivity in farms if mixed-sex stocks are cultured. The sexual growth dimorphism must be understood and managed to optimize aquaculture potential, but to date little data on sex-specific growth patterns in controlled environment are available. The objective of this work is to describe sex-specific growth rates in southern flounder from the juvenile stage to market size by tracking individual growth of males and females.
On 8/29/2024, one hundred and twenty 200-day post-hatch (DPH) southern flounder juveniles (mean total length 12.79 ± 2.03 cm, mean weight 24.87 ± 1.15 g) were randomly selected, individually tagged with a full duplex nano 8mm x 1.25mm magnetic PIT tag, and stocked at 20 fish/tank in 6 blue fiberglass tanks (1572 L each) connected to two recirculating systems maintained at a salinity of 25 ppt and a temperature of 26°C. Fish are being fed a sequence of extruded pellets (Skretting, Nutreco; 55% crude protein and 18% lipid) at a rate of 5.24%/body weight/day. Feed ration is adjusted every 7 days to account for growth and biomass change. All fish are measured (total length and body width) and weighed every six weeks. Growth monitoring will continue until fish reach an average Total Length of 12 inch.
Sex will be determined at the end of the experiment by observation of gonad morphology. Growth rates of individual males and females between sampling points and through the experimental period will be estimated using the Thermal Growth Coefficient (TGC) and Specific Growth Rate (SGR). Alternative models will be considered if growth trajectories depart from the simple models used in these two coefficients. ANOVA will be used to test the significance of differences between sexes accounting for replicate recirculating system and replicate tank within system. At the end of the experiment, morphometric and carcass quality traits including gut, visceral fat, gonad, filet and fileting waste yields will be recorded and compared between sexes after correction for allometric growth.