Motility of spermatozoa obtained from testes of Japanese pearl oyster Pinctada fucata martensii

Effects of NH₃ concentration in sea water and pH of sea water on the motility of spermatozoa obtained from testes were examined in the Japanese pearl oyster. Percent motility at 30 s after dilution increased with increasing NH₃ concentration in sea water from 0.75-2.0 mM. When spermatozoa were diluted with sea water containing 0.75 mM NH₃, which is widely used as the insemination fluid in the hatchery of this species, the percent motility increased with time elapsed after dilution, and peaked at 5 min. For spermatozoa diluted with sea water containing 2.0 mM NH₃, the percent motility increased rapidly and peaked at 30 s. The pH of sea water increased with increasing NH₃ concentration from 8.2 (0 mM NH₃) to 9.9 (5.0 mM NH₃). When spermatozoa were diluted with artificial sea water at various pH (buffered without NH₃ at 6.0-10.0), only spermatozoa diluted with artificial sea water of pH 10.0 were motile, and the percent was considerably lower than those in ammonical sea water. These results indicate that sea water containing 2.0 mM NH₃ is a suitable solution for evaluating sperm motility, and that NH₃ and/or ammonium ions may activate sperm motility in this species.