Condition index and chemical composition of meats of Sydney rock oysters (Saccostrea commercialis) and Pacific oysters (Crassostrea gigas) at four sites in Port Stephens, NSW

Abstract

Adult Sydney rock oysters (Saccostrea commercialis) and Pacific oysters (Crassostrea gigas) were kept on commercial oyster leases at three intertidal sites in Port Stephens, New South Wales, and subtidally under an experimental raft at a fourth site between July 1988 and September 1989. Oysters were sampled from each site at approximately monthly intervals for chemical and histological analysis. Condition index and percentage glycogen of Pacific oysters were higher than those of Sydney rock oysters during winter and spring but tended to be lower during summer and autumn. Gonads of Pacific oysters matured two months earlier than those of Sydney rock oysters, with spawning being observed at all sites in October. Sydney rock oysters spawned later during December-January and did not lose as much condition after spawning as Pacific oysters. The absolute amount of glycogen in the meats of both species dropped at the expense of protein and lipid as the oysters became fully ripe. For both species, general condition of the oysters was best when they were grown subtidally under the raft, although both species were badly affected by invasion of the protistan parasite Mikrocytos roughleyi at this site. Poorest overall condition for both species occurred at a site (Karuah River) that experienced decreased salinities and increased turbidity after rain. Highest condition indices were found in Sydney rock oysters, at the site most dominated by coastal conditions (Corrie Island).

Relación del crecimiento, condición y supervivencia del ostión del Pacífico Crassostrea gigas y las variables ambientales, cultivado en suspensión en el sistema lagunar Navachiste-Macapule, Sinaloa, México

“…El índice de condición es una medida muy útil para reconocer el estado nutritivo de los bivalvos debido al cambio temporal de las reservas alimenticias mismas que están influenciadas por la disponibilidad del alimento en conjunción con los factores ambientales (Soniat & Ray 1985), y es ampliamente usado en C. gigas (Mason & Nell 1995, Baghurst & Mitchell 2002. El índice de condición se incrementó hasta mayo y disminuyó en junio y julio, mientras que el patrón de la Cl-a y MOP decreció a partir de mayo, lo cual sugiere que la disponibilidad de alimento pudiera haber afectado el ciclo reproductivo de este bivalvo y se haya presentado un evento de desove, lo cual es similar a lo reportado por Chávez-Villalba et al (2007).…”

A physiological comparison between Pacific oysters Crassostrea gigas and Sydney Rock oysters Saccostrea glomerata: food, feeding and growth in a shared estuarine habitat

“…Both species lost tissue weight in the summer (November 1999to February 2000, possibly related to the annual reproductive cycle, particularly spawning. Mason & Nell (1995) observed that Pacific oysters in Port Stephens spawned in October; Sydney Rock oysters spawned later, during December and January (i.e. summer in Australia).…”

“…Pacific oysters first appeared in large numbers at Port Stephens in the summer of 1984-1985(Nell 1993 and, although first treated as a 'noxious species', approval to farm Pacific oysters was passed in 1991. This species is thought to grow more rapidly than the Sydney Rock oyster (Nell 1991) and with a greater fecundity, thus posing a threat to the native species (Holliday & Nell 1985, Mason & Nell 1995.…”

Spatial Patterns of Wild Oysters in the Hawkesbury River, NSW, Australia

“…Mangrove sites were characterized by Avicennia marina, a species, which produces pneumatophores. Sampling was timed to avoid the peak S. glomerata spawning season, which can introduce variability in tissue condition (Mason & Nell 1995).…”