Development of aquaculture methods for southern flounder, Paralichthys lethostigma: I. Spawning and larval culture

A detailed spawning and larval rearing protocol for the production of southern flounder, Paralichthys lethostigma, is presented. The protocol is based on the results of spawning, larval culture and fingerling production trials with the southern flounder, which were completed during 1998 and 1999. Seventy-six brood fish (0.1-3.8 kg) were collected from the wild, acclimated to captivity, and stocked in maturation tanks. Sex ratio (male:female) was 1.1:1. Males (0.1-1.0 kg; mean = 0.5 kg±0.30 SD) were significantly smaller (P > 000.1) than females (0.5-3.8 kg; mean = 1.8 kg±0.75 SD). Spermatogenesis was achieved using temperature manipulation during a 3-month period. Vitellogenesis was nearly completed when most females were caught, and final ovulation was accomplished using gonadotropin releasing hormone-analogue (GnRH-a) implants and human chorionic gonadotropin (HCG). Eggs were obtained from both tank and strip spawnings. At 24-26°C, fertilized eggs hatched within 24-28 hours. Weaning to artificial diets was completed after 5 weeks, when metamorphosis was completed. Epizootics of Vibriosis and Amyloodinium ocellatum caused massive mortalities. Average survival rate from eggs to fully metamorphosed fingerlings was 30%, ranging from 5-40%. A total of 14, 562 juveniles measuring 5 cm were produced in these experimental trials. Approximately 25% of the fingerlings exhibited pigment abnormalities known as hypomelanosis or pseudo-albinism on the dark side and hypermelanosis or ambicoloration on the blind side. Reversed asymmetry was observed in 5% of the fingerlings and a few individuals (0.02%) exhibited no ocular migration at all. A large size variation was observed during early larval development stages, with larger individuals growing faster through post-larval, juvenile, and adult stages. Results suggest that hatchery production of southern flounder fingerlings should rely on early culling of runts.