The growth and survival of experimental batches of hatchery-reared spat of Ostrea edulis L. and Crassostrea gigas thunberg, using different methods of tray cultivation

Abstract

The seasonal growth and survival of experimental batches of hatchery-reared spat of the European oyster ( Ostrea edulis) and the Pacific oyster ( Crassostrea gigas) was followed in North Wales during the period 1972 to 1975. Three methods of tray cultivation were compared. These were: (a) trays suspended from a raft in the Menai Straits, (b) trays supported on trestles on the foreshore of the Menai Straits, and (c) trays in a laboratory nursery system which were supplied with sea water from Conwy estuary via a pumped storage system. Growth of oysters in the nursery system was consistently inferior to that of oysters kept at either site in the sea. Although in several years there were significant differences between the growth of oysters on the raft and in trays supported by trestles, on average neither site consistently produced larger oysters. Survival was significantly better in the nursery system for both species of oyster, but no consistent differences in survival were observed between either site in the sea. Seasonal growth of both species of oyster as well as the mortality of O. edulis were positively related to temperature. It was concluded on the basis of cost that (i) cultivation in systems employing pumped sea water would not be viable in the long term, and (ii) raft cultivation would only be suitable for post-hatchery sized oysters up to about 5 g live weight.