Sex determination in southern flounder, Paralichthys lethostigma from the Texas Gulf Coast and implications of climate change

In marine flatfish of the genus Paralichthys, temperature plays a large role in sex determination. Thus, global climate change could have significant effects on southern flounder (Paralichthys lethostigma), a commercially and recreationally important flatfish whose populations have steadily declined in Texas in the last 25 years. The most susceptible areas to global climate change are shallow water environments, particularly estuaries, which serve as essential nursery habitats for juvenile southern flounder. While in the estuaries, juveniles develop, and sex is determined. Juvenile southern flounder possess genotypic sex determination; however, the sex of females is highly influenced by temperature and can result in sex reversal. The temperature-sensitive enzyme complex responsible for estrogen biosynthesis in vertebrates is aromatase cytochrome P450 (P450arom), a critical component in ovarian differentiation that can be used to measure presumptive males and females exposed to a gradient of temperatures. This research identifies that sex is influenced by temperature between 35 and 65 mm total length (TL) and establishes that increases in temperature from 18 °C during this size range produce increasingly male skewed sex ratios in southern flounder from Texas. The findings presented here are critical for optimizing production of females in culture and for developing stock enhancement programs of southern flounder in Texas.