CONDITION INDEX AND CHEMICAL-COMPOSITION OF MEATS OF SYDNEY ROCK OYSTERS (SACCOSTREA-COMMERCIALIS) AND PACIFIC OYSTERS (CRASSOSTREA-GIGAS) AT 4 SITES IN PORT-STEPHENS, NSW
Cj. Mason et Ja. Nell, CONDITION INDEX AND CHEMICAL-COMPOSITION OF MEATS OF SYDNEY ROCK OYSTERS (SACCOSTREA-COMMERCIALIS) AND PACIFIC OYSTERS (CRASSOSTREA-GIGAS) AT 4 SITES IN PORT-STEPHENS, NSW, Marine and freshwater research, 46(5), 1995, pp. 873-881
Adult Sydney rack oysters (Saccostrea commercialis) and Pacific oyster
s (Crassostrea gigas) were kept on commercial oyster leases at three i
ntertidal sites in Port Stephens, New South Wales, and subtidally unde
r an experimental raft at a fourth site between Jury 1988 and Septembe
r 1989. Oysters were sampled from each site at approximately monthly i
ntervals for chemical and histological analysis. Condition index and p
ercentage glycogen of Pacific oysters were higher than those of Sydney
rock oysters during winter and spring but tended to be lower during s
ummer and autumn. Gonads of Pacific oysters matured two months earlier
than those of Sydney rock oysters, with spawning being observed at al
l sites in October. Sydney rock oysters spawned later during December-
January and did not lose as much condition after spawning as Pacific o
ysters. The absolute amount of glycogen in the meats of both species d
ropped at the expense of protein and lipid as the oysters became fully
ripe. For both species, general condition of the oysters was best whe
n they were grown subtidally under the raft, although both species wer
e badly affected by invasion of the protistan parasite Mikrocytos roug
hleyi at this site. Poorest overall condition for both species occurre
d at a site (Karuah River) that experienced decreased salinities and i
ncreased turbidity after rain. Highest condition indices were found in
Sydney rock oysters, at the site most dominated by coastal conditions
(Corrie island).