Ovarian Development and Maturity of Southern Flounder in the North-Central Gulf of Mexico

Southern Flounder, Paralichthys lethostigma, is the most commonly harvested flatfish in the north-central Gulf of Mexico (GOM), yet knowledge of the species’ reproductive biology is greatly limited. Our objectives were to estimate length- and age-at-maturity, and to describe reproductive seasonality of female Southern Flounder. We collected fish from September 2014 through February 2016 using various sampling techniques, including hook and line and gigging. We classified maturity histologically for each individual (n = 221) and fit a logistic model to binomial maturity data. The estimate for mean length-at-50%-maturity is 308 mm and mean age-at-50%-maturity is 1 y. We assessed spawning seasonality using both the mean monthly Gonadosomatic Index (GSI) and histological indicators. Mean GSI values were elevated in October and November. Females were in the spawning capable reproductive phase in early November and in the regressing phase in February. These results suggest that the Southern Flounder spawning season occurs from December to February in the north-central GOM. Histological analysis shows that Southern Flounder exhibits asynchronous oocyte development and is a batch spawner. The results of this research provide an improved examination of Southern Flounder reproduction, which will inform future stock assessments for this species.