Diseases causing high mortality occurred in a hatchery for rearing juvenile oysters, C. gigas, at Bicheno, Tasmania, during 1980. Outbreaks of the disease characteristically showed three peaks: in 7-10-day- old larvae, in older larvae several days before setting, and in spat 1-2 weeks after setting. Various marine bacteria were cultivated from inactive larvae and other hatchery specimens, and the predominant strains were identified. When given to normal young larvae at doses of 1 × 105-5 × 105 or 1 × 10-5-5 × 107 bacteria (total dose), seven strains (five strains of Vibrio, two strains of Alteromonas) caused fatal infections in most animals. This is the first report of pathogenic marine bacteria in an Australian shellfish hatchery.

Growth of Pacific oyster spat caught commercially in intertidal zones of the River Tamar was monitored for 6 months. After 90 days Tamar spat had a mean length of 14.3 mm. Reduced growth rates with falling water temperatures were noted. Oysters transferred to the Pipeclay Lagoon lease grew to 75 mm length and 52 mm width in only 12 months. Average live weight was 42.8 g and drained flesh weight 6.3 g. Seasonal differences in growth were apparent with major shell increases in autumn months. Shell width increased preferentially over length in winter but thereafter was always less. In contrast to other reported studies, summer growth rates were markedly reduced. Exposure to high air temperatures coupled with reproductive activity may be responsible. Growth of oysters during the second year on the growing lease was reduced but followed similar patterns to the previous year. At termination of study, 28-month-old oysters averaged 89.9 mm length and 61.7 mm width, had a live weight of 69.1 g and a drained flesh weight of 13.3 g.