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 artifici al photothermal regimes: (1) natural regime, simulating natural habitat con ditions; and (2) accelerated thermal regime, with seasonal temperature chan ges advanced by one month. A third group of fish was held in outdoor tanks under ambient photothermal conditions. Under all photothermal conditions, o nset of vitellogenesis was associated with declining daylength and temperat ure, beginning in the accelerated group, then progressing to the natural an d the ambient groups. From 20 September to 28 November 1995, 23 vitellogeni c stage females from the accelerated and natural regimes were implanted wit h a cholesterol-cellulose pellet containing LHRH-a (100 mu g/kg body wt). F emales 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 f emales were spawned twice during the study period by LHRH-a pellet implanta tion. Infrequent, natural spawning without hormone intervention was also ob tained. Females released from 22.7-396.9 x 10(3) eggs on the first day of s pawning, with fertilization and hatching rates of 0-93.4% and 0-81.1%, resp ectively.