Broodstock management and spawning of southern flounder, Paralichthys lethostigma

Collaborative studies are underway in South Carolina (SC) and North Carolina (NC) to control reproduction of southern flounder, Paralichthys lethostigma. Although cultured broodstock are being developed, work to date has been with wild caught adults held in captivity for at least 1 year. Shortly after capture, wild adults should be treated to control diseases and parasites, especially Amyloodinium sp. and fish lice, Argulus sp. Induced spawning using only photothermal control has not occurred, but GnRHa implants have been successfully used to induce ovulation and allow strip-spawning. In addition, during 1997, photothermal conditioning coupled with 100 μg GnRHa implants resulted in successful tank-spawning. During a 99-day period, eggs were collected on 64 days and lowering temperature was shown to inhibit spawning. On days that spawning occurred, mean number of eggs collected was 277,844 (±177,714) and mean fertility was 32.8% (±25.2%). Total number of eggs collected was 17,782,000. Females used in the study were ≥5 years old while the males were ≥3 years old. Fish had been in captivity for ≥1.5 years. The spawning success achieved using the combination of photothermal conditioning and GnRHa implants resulted in less stress to the fish, higher egg production and an extended spawning period. Use of photothermal conditioning coupled with tank-spawning techniques should allow year-round spawning of southern flounder. This should facilitate more rapid development of a culture technology for this species.