Broodstock management and spawning of southern flounder, Paralichthys lethostigma

Collaborative studies are underway in South Carolina (SC) and North Carolin a (NC) to control reproduction of southern flounder, Paralichthys lethostig ma. Although cultured broodstock are being developed, work to date has been with wild caught adults held in captivity for at least 1 year. Shortly aft er capture, wild adults should be treated to control diseases and parasites , especially Amyloodinium sp. and fish lice, Argulus sp. Induced spawning u sing only photothermal control has not occurred, but GnRHa implants have be en successfully used to induce ovulation and allow strip-spawning. In addit ion, during 1997, photothermal conditioning coupled with 100 mu g GnRHa imp lants resulted in successful tank-spawning. During a 99-day period, eggs we re collected on 64 days and lowering temperature was shown to inhibit spawn ing. 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 e ggs collected was 17,782,000. Females used in the study were greater than o r equal to 5 years old while the males were greater than or equal to 3 year s old. Fish had been in captivity for greater than or equal to 1.5 years. T he spawning success achieved using the combination of photothermal conditio ning and GnRHa implants resulted in less stress to the fish, higher egg pro duction and an extended spawning period. Use of photothermal conditioning c oupled with tank-spawning techniques should allow year-round spawning of so uthern flounder, This should facilitate more rapid development of a culture technology for this species. (C) 1999 Elsevier Science B.V. All rights res erved.