Nursing of white scar oyster spats, Crassostrea belcheri (Sowerby) at various flow rates in recycled and free-flow upwelling systems
1997
Tanate Poomtong
Nursing of White Scar Oysterspat, Crassostrea belcheri (Sowerby) for a period of nine weeks in an upwelling system at flow rates of 10, 50, 100 and 150 ml/min/gm was conducted to determine the optimum flow rates and nursing duration. The study comprised two experiments. In the first experiment, the spats of 1 mm length were cultured in a recycled upwelling system and were harvested when the size was 5 mm. The spats of 5 mm length were cultured in a free-flow upwelling system and were harvested when the size was 10 mm in the other experiment. In each experiment, the spat weight, shell length and numbers of harvested spats cultured at different flow rates were compared. The first experiment showed that the suitable flow rate of the recycled upwelling system was between 50 and 100 ml/min/gm with a survival rate of 16 percent. Results of the response surface analysis revealed that the optimum flow rate was 85 ml/min/gm and the suitable nursing duration was 6 weeks. It was found that suitable flow rate in the free-flow upwelling system was between 100 and 150 ml/min/gm with a survival rate of 50 percent. The optimum flow rate obtained from the response surface analysis was 114 ml/min/gm and the suitable nursing duration was 5 weeks. In both recycled and free-flow upwellng systems with flow rates of 10 and 50 ml/min/gm, the spats grew due to inadequate food. The growth was suppressed at the flow rate of 150 ml/min/gm as the rapid flow rate disturbed food intake of the spats.
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