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The reproductive cycle of Pecten sulcicostatus is described as part of an investigation into the potential commercial culture of this species in South Africa. Scallops were collected monthly from False Bay, from August 2004 to October 2005, to determine seasonal variation in the gonadosomatic index (GSI) and to assess associated histological changes within the gonads. The reproductive cycle of P. sulcicostalus demonstrated clear seasonality. The mean GSI was highest from June to September (winter to early spring), and lowest from November to January (late spring to summer). The GSI findings were corroborated by histological analysis of the gonads with the mean oocyte diameter reaching a maximum in August and a minimum in November. Seasonal stratification and corresponding changes in phytoplankton biomass are considered to control the reproductive cycle of P. sulcicostatus in False Bay as winter spawning and the subsequent decline in the GSI coincide with the transition to spring upwelling conditions and a decline in bottom water temperature and food availability. [ABSTRACT FROM AUTHOR]

Protein, total lipid, and carbohydrate were measured for spawned eggs, D-shaped larvae, premetamorphic, and metamorphic larvae of the bay scallop Argopecten irradians concentricus (Say). Spawned eggs were composed of 64.0% protein, 26.5% lipid, and 9.5% carbohydrate. After 48 hours of embryogenesis, 13.6% of the protein, 46.3% of the lipid, and 20.8% of the carbohydrate mass had been lost, providing 25.5%, 69.8%, and 4.8% of the total energy expenditure of 0.176 mJ per embryo. During 48 hours of metamorphosis, lipid was utilized first, followed by a heavy consumption of protein; protein, lipid and carbohydrate lost 55.6%, 59.4%, and 67.3% of their mass respectively. Protein and lipid supplied a comparable amount of energy for metamorphosis, 47.9% and 43.5%, respectively; whereas, carbohydrate contributed only 8.6%, to the 4.35 mJ per larva metamorphic energy expenditure. [ABSTRACT FROM AUTHOR]

Rates of oxygen consumption and ammonia excretion were determined at 25 °C for larval and juvenile bay scallops Argopecten irradians concentricus. Oxygen consumption rate (Vo2, μIO2 h-1) varied with body size ash-free dry weight (AFDW, mg) according to the relation Vo2 = 7.199 AFDW0.921 for larvae and Vo2 = 2.142 AFDW0.905 for juveniles. Mean weight-specific Vo2 ranged from 14.66 to 15.84 μIO2 mg AFDW-1 h-1 for larvae and from 1.80 to 5.28 μIO2 mg AFDW-1 h-1 for juveniles. Weight-specific Vo2 declined with increasing body size at > 2 mm shell height but became independent of body size at > 2 mm shell height. Swimming was estimated to cause 8 to 29% of the total larval oxygen demand. In juveniles of 3.5 to 5.0 mm shell height, Vo2 increased as temperature increased from 15 to 30 °C, being 1.24 ± 0.35, 1.77 ± 0.70, 2.33 ± 0.85., and 2.74 ± 0.57 μIO2 mg AFDW-1 h-1 at 15, 20, 25 and 30°C, respectively. The Q10 was 2.99 at 15 to 20°C, 1.74 at 20 to 25 °C and 1.37 at 25 to 30°C. Ammonia excretion rate (U, μgNH4-N h-1) increased with body size following the equation U = 0.161 AFDW0.928. Energy loss through ammonia excretion was equal to 1.5 to 3.7% and 13.5 ± 2.8% of the respiratory energy loss in larvae and juveniles, respectively. [ABSTRACT FROM AUTHOR]

Incorporation of 14C into lipid, carbohydrate, and protein fractions of digestive gland, adductor muscle, and ovary body components of the bay scallop, Argopecten irradians concentricus(Say), varied seasonally in conjunction with oogenesis. Resting stage scallops (June-July) were characterized by net radiocarbon losses in ovary fractions. Nutrient storage during this period was indicated by relatively small radiocarbon losses in digestive gland fractions that were equaled by gains in adductor muscle carbohydrate and protein fractions. During the period of oocyte growth (August-October) 14C losses in digestive gland and adductor muscle fractions always exceeded progressive gains in the ovary. Increased carbon turnover (catabolism) of digestive gland lipid and adductor muscle carbohydrate fractions accompanied decreased turnover (anabolism) of ovary lipid, indicating the utilization of these reserves for the production of ova. After spawning (November), 14C was lost from all body component fractions, indicating a state of negative energy balance and generally poor physiological condition. These results directly reinforce the pattern of energy storage and utilization in A. irradians concentricusindicated by previous studies on growth, biochemical composition, and substrate catabolism.