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Abstract
The objective of the present study was to determine the optimal dilution rate, osmotic pressure and cation concentrations on sperm motility of Crassostrea gigas. Semen was diluted in artificial seawater at different ratios (1:50, 1: 100, 1: 150 and 1: 200) to find the best dilution ratio for sperm motility. Then, the best dilution rate from this experiment was applied for osmotic pressure tests (concentrations of 300, 400, 500, 600 mOsm/kg) and effect of cations Na+, Ca²+, K+, Mg²+ (concentration 0, 2, 0.4, 0.6, 0.8M). Each observation was repeated 3 times. The results indicated that the best performance of Pacific oyster sperm were remarkable at the dilution rate 1: 200; osmolality 500 mOsm/kg and the cation concentrations of Na+ and K+ 0.4M, Ca²+ 0.2M. In the presence of Mg²+, sperm of Pacific oyster were not active at any concentrations in the study. The highest fertilization rates was observed when artificial inseminating in artificial seawater, followed by the treated natural sea water, than by a 500 mOsm/kg osmotic pressure solution and the lowest in Na+0.4M solution with respectively the result are 75.77 ± 5.26%; 71.78 ± 3.25%; 49.94 ± 2.12%; 35.8 ± 5.27%.
Key words: Pacific oysters, dilution ratio, osmolality, cation concentration, sperm motility