Temperature and photoperiod induced maturation of southern flounder

Southern flounder (Paralichthys lethostigma) were maintained either in a 9500-L or 2300-L recirculating tank system from October 1983-March 1986 and subjected to controlled photoperiod and temperature conditioning to induce spawning. The fish were first subjected to a 6-month regime to delay natural spawning until spring (1984) followed by 6-month and 4-month regimes to induce either early fall (1984) or late summer (1985) spawning. Regardless of the conditioning regime, female gonadal development and egg release occurred only during December-February when water temperature was 18C and photoperiod maintained at 9-h light: 15-h dark. Male spermatogenesis coincided with female ovarian development but they did not fertilize eggs. The number of eggs released ranged from 66 to 28,900. Injection of 125 g LHRHa/fish failed to induce male courtship and fertilization. Strip-spawning attempts were also unsuccessful because eggs could not be manually extruded despite the presence of hydrated ova within the ovaries.