The objective was to design and evaluate a Suspension oyster tray unit to optimize conditions necessary for successful commercial culture of oysters in British Columbia for the half-shell market. The suspension system was tested against MacNicol and Nestier trays presently used by the industry. Units were located in two sites in Trevenen Bay. One location was sheltered and calm; the other a natural tidal raceway with intense current flow. The purpose was to test the ability of the design to provide more uniform growth, retard fouling, be easily handled and be commercially feasible to construct. Assessing tray performance was based on monitoring shell growth, condition index, fouling occurrence, materials handling and the capital costs of the systems. Field-experimentation began in June and terminated in October, 1979. The Nestier unit had the best shell growth in the calm environment but displayed variation in growth among trays in the stack, suffered retarded growth in the tidal raceway and had significant barnacle accumulation. The MacNicol performed on par with the Suspension system except for variations in growth due to vertical position, the accumulation of mussels and lowered performance at the tidal raceway site. Suspension tray units performed similarily at both sites, exhibited less variation in growth among trays in a stack, retarded fouling and proved the most economically feasible system for commercial use. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Use of antibiotics in the aquaculture industry for the control of bacterial infections in salmon has led to public concern regarding antibiotic residues in salmon tissue and the potential health risk this poses to humans. Oxytetracycline and Romet-30 are two common antibacterial agents utilized to control disease in the local finfish aquaculture industry of British Columbia, Canada. Many fish farms in British Columbia are located within close proximity to existing shellfish stocks. The potential for antibiotic bioconcentration and the production of bacterial resistance to the drugs in bivalves is a concern. The development of a solid phase extraction technique for these two drugs from Pacific oysters, Crassostrea gigas was accomplished. Analysis of whole oysters via HPLC revealed detectable levels of oxytetracycline and Romet-30 up to 4 weeks after antibiotic treatment at the salmon farm site. Oysters suspended in the salmon net pens and surrounding waters were sampled over a 5 month period. Concentration of oxytetracycline residues in oyster tissue reached a maximum of 0.11 ppm (n=2). Levels of sulphadimethoxine in oyster tissue reached a maximum concentration of 1.27 ppm (n=2). Maximum detectable concentrations of ormetoprim in oysters were 0.26 ppm (n=2). A controlled study investigating uptake and depuration of oxytetracycline and Romet-30 in the Pacific oyster revealed results similar to those described for the salmon farm. A flow through drug delivery system for the Pacific oyster was utilized over a ten day uptake and thirty day depuration period. Levels of oxytetracycline in whole animal tissue increased in a linear fashion (r²=0.984) over the uptake period. This indicates that the drug was bioaccumulated in the oyster reaching a maximum concentration of 10.72 ± 2.4 s.e. ppm (n= 3) on day 10 of uptake. Depuration of the drug was rapid. After thirteen days a concentration of 0.21 ± 0.04 s.e. ppm (n=7) was detected. The detection of Romet-30 in the uptake and depuration in the oyster was more erratic. Day 7 of uptake revealed a maximum concentration of sulphadimethoxine and ormetoprim of 1.092 ± 0.24 s.e. ppm (n=7) and 0.21 ppm (n=3) respectively. Depuration of Romet-30 was rapid. The concentration decreased to 0.029 ppm (n=3) by day 13. Condition indices of oysters sampled before and after antibiotic treatment indicated a significant increase (p<0.05) in condition index after treatment with medicated feed. A quantitative survey of bacteria associated with the gut of the oyster was performed. Relative numbers of endogenous bacteria were compared to oysters before and after antibiotic treatment. Numbers of bacteria significantly decreased (p< 0.05) following treatment. / Land and Food Systems, Faculty of / Graduate