SOME BIOCHEMICAL AND PHYSIOLOGICAL ASPECTS OF GROWTH AND GAMETOGENESIS IN CRASSOSTREA-GIGAS AND OSTREA-EDULIS GROWN AT SUSTAINED ELEVATED-TEMPERATURES

Crassostrea gigas (Thunberg) and Ostrea edulis L. were grown at sustained temperatures of 12°, 15°, 18° and 21 °C for a period of 19 weeks. Regular assays of weight specific ammonia excretion rate were made, following which animals were sacrificed for estimation of dry meat weight, dry shell weight, biochemical composition (percentage carbon, nitrogen, carbohydrate, ash) and gonadal development (histological assessment). Crassostrea gigas grew from an intial live weight of 5.2 g to values of 23.5, 28.2, 34.6 and 38.7 g at 12°, 15°, 18° and 21 °C respectively. However, dry meat weight was not positively related to temperature: from an initial value of 88.7 mg, final values of 1736, 1253, 1322 and 1219 mg were recorded at 12°, 15°, 18° and 21 °C respectively. Ostrea edulis exhibited increases in both live weight and dry meat weight which were proportional to experimental temperature. Live weight increased from an initial value of 4.1 g to 10.6, 13.6, 19.3 and 22.3 g at 12°, 15°, 18° and 21 °C respectively. Dry meat weight increased from an initial value of 95.0 mg to 444.5, 566.0, 617.0 and 756.0 mg at 12°, 15°, 18° and 21 °C respectively. An initial increase in percentage carbohydrate was observed at all temperatures in both species. In C. gigas this was followed by a decrease in carbohydrate content which was closely related to the late active stage of gametogenesis. The transition from an increase to a decrease in percentage carbohydrate occurred earlier at higher temperatures. In O. edulis no marked decrease was noted in the percentage carbohydrate content despite marked gametogenic activity. No evidence of hermaphroditism was found in C. gigas. Twenty-seven per cent of O. edulis examined contained sex products of both sexes at various stages of development. Ripe gonads developed in both species at all temperatures. However, C. gigas spawned only at 18° and 21 °C, and O. edulis spawned only at 15, 18° and 21 °C. Ammonia excretion data exhibited an allometric relationship (E = aWb) with weight prior to spawning in both species at all temperatures. After spawning an increase in weight specific excretion rate was observed. © 1979, Marine Biological Association of the United Kingdom. All rights reserved.