Southern Flounder (Paralichthys lethostigma) are distributed throughout inshore waters along the Southeastern Atlantic and Gulf of Mexico coastline. They have been heavily targeted by fisherman 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. One such area the Department has focused on is spawning through evaluation of potential hormones for spawning induction.
From January through March of 2024, staff at the Waddell Mariculture Center and Marine Resources Research Institute evaluated the efficacy of multiple spawning hormones including Ovaprim®, Ovaplant-Liquid, and a type II gonadotropin releasing hormone analogue (GnRH IIa). All three hormones were administered to female Southern Flounder at a standard dose of 10 µg/kg. An individual female (n = 12) of each treatment was paired with a single male and observed for spawning up to 120 hours post administration. Females were also assessed at 48 and 72 hours post administration to determine if eggs could be stripped from females. Standard artificial fertilization protocols were applied for all strip spawns. Spawning frequency, egg output, and egg and larval viability parameters were recorded for every spawn.
All hormones were effective at inducing females to spawn volitionally as well as be stripped of eggs, with no significant differences detected in spawning frequency. However, floating egg output was significantly higher for stripped females administered Ovaplant-Liquid (62.51 ± 8.25 eggs/g) in comparison to females administered GnRH IIa (31.34 ± 6.56 eggs/g), but similar to Ovaprim® (49.88 ± 6.95 eggs/g). In addition, hatching success of floating eggs stripped from females was significantly higher for females treated with Ovaplant-Liquid or Ovaprim® (51.54 ± 1.47% and 50.37 ± 1.47%, respectively) compared to those treated with GnRH IIa (39.46 ± 1.41%). Overall, more fertile eggs were produced from Ovaplant-Liquid or Ovaprim® treated females compared to GnRH IIa by the conclusion of the experiment. These results will ultimately lead to better production protocols for spawning Southern Flounder in captivity.