Progress in controlled maturation and spawning of summer flounder Paralichthys dentatus broodstock

Wild-caught, adult summer flounder Paralichthys dentatus (avg. wt. = 740 g; range = 264-1,540 g; N = 60), collected in northeastern, US coastal waters during October 1994, were transported to Vero Beach, Florida in March 1995 and held in 2.6-m(3) indoor tanks through November 1995 under two artificial photothermal regimes: (1) natural regime, simulating natural habitat conditions; and (2) accelerated thermal regime, with seasonal temperature changes advanced by one month. A third group of fish was held in outdoor tanks under ambient photothermal conditions. Under all photothermal conditions, onset of vitellogenesis was associated with declining daylength and temperature, beginning in the accelerated group, then progressing to the natural and the ambient groups. From 20 September to 28 November 1995, 23 vitellogenic stage females from the accelerated and natural regimes were implanted with a cholesterol-cellulose pellet containing LHRH-a (100 mu g/kg body wt). Females with initial mean oocyte diameters ranging from 258-456 mu m spawned voluntarily 2.5-5.5 d postimplantation, while no maturational response was obtained from females with mean diameters ranging from 165-231 mu m. Two females were spawned twice during the study period by LHRH-a pellet implantation. Infrequent, natural spawning without hormone intervention was also obtained. Females released from 22.7-396.9 x 10(3) eggs on the first day of spawning, with fertilization and hatching rates of 0-93.4% and 0-81.1%, respectively.