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Six yeast species, cultured on both glucose and acetate as carbon sources, and three dry yeast-based diets (Microfeast ® ) were compared as potential algae substitutes for feeding Sydney rock oyster spat. At the 80% substitution level, two of the dry yeast-based diets containing 7.6 and 21.5% total lipid gave 72 and 76%, respectively, of the dry spat weight gain obtained with the algae-fed control. Weight gains of 58–67% of that of the algae-fed control were also obtained with the following live yeast diets: Dipodascus capitatus and Candida utilis cultured on either glucose or acetate, and Saccharomyces cerevisiae cultured on glucose. There was a negative correlation between the increase in spat dry weight and nitrogen free extract ( r = −0.58; y = 30.34 − 0.26 x ; P r = 0.51; y = 6.10 + 0.31 x ; P

Four breeding lines of Sydney rock oysters, Saccostrea commercialis, progeny of parents selected for faster growth for one generation, were compared in a 17-month experiment with two control lines (spat produced from non-selected oysters). Oysters from two out of four selection lines were significantly heavier (P < 0.05) than the controls. The improvements in weight gain for the two selection lines grown loose on trays were 2.9 and 8.5%, and for the two slat lines (grown fixed on PVC slats) they were 0.0 and 5.0% for the first generation of selection. These results provide encouragement for the selective breeding of Sydney rock oysters for weight gain.

The biochemical compositions of seven strains of marine bacteria and six strains of yeast—all isolated from an Australian waterway—were compared with two well-studied yeast strains, Candida utilis and Saccharomyces cerevisiae , to assess their nutritional quality for bivalve aquaculture. Protein was a major constituent of both yeast and bacteria (25–49% dry weight), with lipid a minor component (2.5–9.0%). Carbohydrate in yeast was 21–39% of dry weight, bacteria had 2.5–11%. Ash ranged from 4.7 to 14% dry weight in 11 of the yeast and bacteria strains; the remaining species, all bacteria, had high levels (29–40%). Nucleic acid ranged from 3.3 to 8.4% dry weight in the yeast and bacteria. The amino acid compositions were similar in the strains, and closely matched those of Saccostrea commercialis larvae and spat indicating a high protein quality. Glucose was a major sugar in the polysaccharide of both yeast and bacteria (12–73% of total sugars); mannose was in high concentrations in the yeast (24–65%). Both polyunsaturated fatty acids (PUFAs) 20:5 n − 3 and 22:6 n − 3 were absent in all strains, and thus if the strains are to be used in bivalve aquaculture, they would need to be supplemented with live algae rich in these PUFAs. High levels of good quality protein, however, indicate their potential to provide important nutrients in a mixed diet.

A culture method (‘slats’) being used to compare Sydney rock oysters ( Saccostrea commercialis ) for growth rate selection was further evaluated. In this method, oysters are affixed to plastic slats in a matrix pattern. The presence of non-random positional effects associated with an oyster's location within the tray compartment and the impact of their removal was investigated in terms of row and column effects and band effects. Within each tray compartment, oysters were assigned to different ‘bands’ according to their distance from the side of the compartment. The effect of the presence or absence of outliers in the estimation of row, column and band effects was also investigated. The growth rate of oysters was found to be sensitive to apparently small environmental differences. There were substantial and statistically significant row, column and band effects for two of the three growing sites. These non-random positional effects were effectively removed by adjusting individual oyster weights on the basis of row and column means, irrespective as to whether these means had been estimated in the presence or absence of outliers. Data adjusted on the basis of band means tended to retain some substantial row and/or column effects. There was little, if any, additional advantage in adjusting the row and column adjusted data for band effects.

Four growing methods for Sydney rock oysters, Saccostrea commercialis, were evaluated for use in a breeding program to select for greater weight increase and improved disease resistance. These methods were: (1) oysters attached and grown on PVC slats (“slats”), (2) oysters attached and grown on tray mesh (“mesh”), (3) culchless (single and loose) oysters grown individually in chambers (“rings”), and (4) culchless oysters grown together in tray compartments (“loose”). The oysters in all growing methods were contained in tarred wooden framed trays covered with polyethylene mesh and supported intertidally on wooden rails. Oysters were individually measured for whole weight (the primary selection criterion), as well as for shell height, length and width. Both “mesh” and “rings” methods were found to be unsuitable for the breeding program because the oysters in these gained little weight. In addition, the shells of the oysters on “mesh” grew through the mesh, and those in the “rings” often grew onto the chamber wall. Oysters grown on slats were significantly (P < 0.05) heavier, had higher and longer shells and a significantly (P < 0.05) lower coefficient of variation for whole weight and shell height than “loose” oysters.

To assess the potential for hatchery production of the venerid clam, Tapes dorsatus , diploid and triploid clams were produced and ongrown until the spat reached 5–8 mm in size. Triploidy percentages at metamorphosis that ranged from 56 to 85% were induced using a 15-min exposure to 1 mg/l cytochalasin B. No differences were observed in the growth rate of sibling diploid and triploid T. dorsatus larvae. Survival of diploid clams to pediveliger stage was however higher. Post-metamorphic growth and survival of diploid and triploid clams remained the same until the clams were removed from the hatchery to outdoor nurseries. Throughout the larval and early spat phases of production, T. dorsatus growth was similar to that reported for the Manila clam, Tapes philippinarum . Based upon its ease of culture, rapid growth and marketability, T. dorsatus are thought to have considerable aquaculture potential.

A two-and-a-half-year study was conducted to compare the performance of sibling diploid and triploid Sydney rock oysters Saccostrea commercialis (Iredale and Roughley) at three intertidal and one subtidal site in Port Stephens, New South Wales (N.S.W.). The triploid Sydney rock oysters were on average 41% heavier than their diploid siblings after 2.5 years of growth. The triploid oysters also maintained higher dry meat weight and higher condition index (CI) values than their diploid siblings at all sites during the final 10 months' growth to market size (40 to 60 whole weight). The triploid oysters at the subtidal site had the highest CI values recorded in this study. When exposed to the protistan parasite Mikrocytos roughleyi which causes winter mortality disease, no differences in mortality between diploid and triploid groups occurred. These findings have major implications for the N.S.W. oyster industry as triploid Sydney rock oysters can reach market size 6–18 months faster and maintain better meat condition than diploid oysters without an increased risk of winter mortality.

Broodstock of the venerid clam Katelysia rhytiphora (Lamy) and of the Sydney cockle Anadara trapezia (Deshayes) were induced to spawn using temperature fluctuations. Larval cultures of K. rhytiphora contained D veligers (97.1±3.7 μm shell width) within 48h, umbonate larvae by day four and pediveligers by day 11. On day 12, pediveligers (198.3±5.39 μm shell width) were placed on settlement screens and allowed to metamorphose over the following 9 days. Larvae of A. trapezia developed to D veliger stage (92.0±3.3 μm shell width) after 48 h and had reached pediveliger (approx. 220 μm) on day 14, at which time they suffered catastrophic mortality.

Two size grades (13.5 and 18.2 mm average shell length spat−1) of juvenile Sydney rock oysters, (Saccostrea commercialis Iredale & Roughley) were grown at a range of stocking densities (0.5 to 6.0 l of oysters cylinder−1) in PVC cylinders for 3 months. Cylinders were deployed on horizontal hardwood frames on an intertidal lease, where they rotated in response to changes in tidal level. For each grade, spat mortality was similar (P > 0.05) for stocking densities of 0.5 to 4.0 l cylinder−1 (mean ± s.e. 11.7 ± 1.1% and 22.5±2.3%, respectively) but higher for the larger grade (33.3 ± 1.7%; P 0.05). Biomass gain and volume of oysters both increased with increasing stocking density (P 0.05). For both grades, coefficient of variation for weight gain and shell length increase data increased (P < 0.001) with density. For maximum growth and minimum coefficient of variation for weight gain and shell length increase, 0.2 and 0.4 g spat should be stocked at low densities of 0.5 or 1.0 l cylinder−1. To optimise biomass gain, while minimising growth reductions and size variation, 0.2 and 0.4 g spat should be stocked at densities of 2.0 and 3.0 l of oysters cylinder−1, respectively.

Juvenile Sydney rock oysters (Saccostrea commercialis) were fed diets composed of either one of twelve algal species or one of eleven algal species in combination with Skeletonema costatum. When used as the sole diet for 21 days, the diatoms Skeletonema costatum, Chaetoceros calcitrans. Chaetoceros gracilis and Thalassiosira pseudonana produced the greatest live weight increase in spat. When Skeletonema costatum was fed in combination with the remaining eleven algal species for 19 days, diets including Chaetoceros gracilis, Tetraselmis chui and Tetraselmis suecica produced the highest live weight increases. These findings indicated differences in the food value of several algal species to larvae and spat of the Sydney rock oyster.

A microencapsulated artificial diet was assessed against a standard diet of micro algae in rearing larvae of the Sydney rock oyster, Saccostrea commercialis (Iredale & Roughley). Unfed control larvae did not develop beyond the straight-hinge stage during the 8-day experiment, whereas those receiving exogenous nutrients, either microalgae or the artificial diet, reached umbone stage. The artificial diet supported larval growth in excess of 80% that of algae-fed larvae in terms of shell length increment; however, there was no significant difference in ash-free dry weight increment between larvae fed the artificial diet and those fed microalgae. Dissolved yeast extract did not enhance larval growth when used as a supplement to the microcapsules. The relative growth rates obtained are the best to date for oyster larvae reared on an artificial diet. The artificial diet used will serve as a benchmark for future nutritional studies with S. commercialis larvae, allowing further development of artificial diets for this species.

Six algal species were fed singly and in combination with Pavlova lutheri , in both fresh and concentrated form, to 1-day-old Sydney rock oyster, Saccostrea commercialis , larvae for 6 days. Although a number of algal species produced high larval length increases, the best fresh diet consisted of P. lutheri and Isochrysis aff. galbana (T-iso). However, when concentrated to a paste and stored for 7–14 days at 4 °C, a combination of P. lutheri and Chaetoceros calcitrans produced greater length increases than any other fresh or stored, single or combined diet tested. Centrifugation and storage of algae prior to feeding had varied effects on the algal species tested, but it had no detected deleterious effects on any of the diatoms tested.

Growth rates of juvenile Sydney rock oysters ( Saccostrea commercialis ) declined with increasing stocking density ( P 2 ) for oysters with average initial whole weights of 0.09, 1.15 and 1.56 g/oyster were obtained at densities of 15 200, 7200 and 3600 oysters/m 2 , in that order. The estimated survival rate of oysters during the 12-month study was high (97.5%).

Gelatin-acacia microcapsules were not adequate as a complete diet for Saccostrea commercialis larvae but were useful as a dietary supplement at a concentration of 0.05 mg/l (1330 microcapsules/ml), and reduced the requirement for microalgae. The inclusion of cod liver oil in the microcapsules was found to produce better growth rates than squid or modified fish oil, both of which contained higher concentrations of the C22:6ω3 and C20:5ω3 fatty acids. Algal meal, a dried extract of Dunaliella salina (Teodoresco), fed at 0.123 mg/l was equal to the microcapsules fed at 0.05 mg/l as a dietary supplement.

This research was undertaken to evaluate triploid Pacific oysters under Tasmanian environmental conditions using local commercial growout techniques. Diploid Pacific oysters were strip spawned in February 1990, and diploid and meiosis 2 triploid larvae reaued from the same pool of gametes. Cytochalasin B (0.5 mg -1 for 20 min) was the triploidy induction stress used. After setting, the oyster spat were held onshore in upwellers and then offshore in intertidal sectionalised trays. From August 1990 they were grown intertidally at three commercial leases in oyster bags within 6 mm mesh baskets and then free in 12 mm baskets. At all sites triploids (76% triploidy) maintained marketable meat condition during the summer - autumn spawning period after attaining commercial size (about 60 g whole oyster weight). At the two sites where diploid oysters spawned they remained in much poorer condition than triploids for at least 4 months post spawning. At two sites oysters reached commercial size, as they approached 2 years of age and at the other site at 3 years of age. Triploid oysters grew faster than diploids as they approached commercial size and were 23.4% larger than diploids on a whole weight basis at the two better sites (age 27 months) and 19.6% larger at the poorest site (age 38 months). At the two better sites mortality of diploid and triploid oysters was negligible during growout. At the third site mortality of triploid and diploid oysters (excluding sampling and whole bags lost through storm damage) averaged 1.0 and 0.3% per month respectively, during growout through April 1993. A greater proportion of the cross sectional area of oyster meat was occupied by gonad in diploids (maximum of 47.7 to 72.6%, depending on site) than in triploids (maximum of 7.7 to 1.9%). Similar maximum glycogen reselves were developed by triploids (15.6 to 21.2 g 100 g -1 dry meat, depending on site) and diploids (14.5 to 20.2 g 100 g -1 dry meat). Triploids maintained these reserves whereas diploids sacrificed most of their glycogen as they approached the spawning season. Triploid Pacific oysters show great promise for overcoming marketing problems caused by poor meat condition of diploid oysters in summer and autumn in Tasmania. However, to exploit this marketing niche, most of the triploids would need to be marketed at about 2 to 2.5 years of age and shell growth rates may have to be repressed through use of elevated growing heights. This should ensure that the oysters do not become too large or that rapid shell growth during the maturation and spawning season does not reduce their condition index advantage over diploids.

Sydney rock oysters ( Saccostrea commercialis ) were fed diets supplemented with soluble whey protein concentrate (WPC) or bacterial protein “Pruteen”. In experiment 1 oysters were fed three diets containing crude protein (CP, N × 6.38) as WPC at levels of 0, 150 and 300 g/kg dry diet. Whole oyster and underwater shell weight gains decreased as the dietary WPC levels increased. The weight gain data suggest that dissolved protein is not efficiently utilised by Saccostrea commercialis . In experiment 2, oysters were fed five diets containing CP (N × 6.25) as bacterial protein “Pruteen” at levels of 0, 171, 340, 511 and 681 g/kg dry diet. Whole oyster and wet-meat weight gains were highest and meat composition was greatly improved (dry matter and glycogen contents increased) with 171 g CP/kg dry diet.

Larvae of the Sydney rock oyster ( Saccostrea commercialis ) were stimulated to undergo metamorphosis and settle in concentrations of 8–12 mM potassium chloride in seawater. At higher potassium chloride concentrations settling rates were reduced. A concentration of 3.14×10 −3 mM CuCl 2 increased the settling rate on the first day, but after 5 days, settling rates were lower than the control and remaining larvae had died.

Sydney rock oyster larvae had the highest growth rates at salinities of 23–39‰, and survival rates at 27–39‰. Two groups of Sydney rock oyster spat with average initial weights of 1.3 mg and 0.61 g grew best at salinities of 25–35‰ and 20–40‰, respectively. The equivalent optimum salinity ranges for the growth of Pacific oyster larvae, 1.1 mg spat and 0.68 g spat were 19–27, 15–30 and 15–45‰, respectively. Salinity had no significant effect ( P >0.10) on survival of spat of either species.

Sydney rock oysters ( Saccostrea commercialis ) were fed an artificial diet at 0, 3, 6, 9, 12 and 15 mg dry food/l. At 9 mg/l oyster glycogen content, condition indices and meat weight gains were maximised without increasing mortality rates. In a comparison of fattening procedures, oysters held in a fertilised pond and those fed a second artificial diet fattened in 4 and 6 weeks respectively, whereas those held in an estuary did not fatten at all. The artificial diet produced higher oyster meat glycogen contents than the fertilised pond and estuary treatments.