Development of a spectrophotometric technique for sperm quantification in the spermcasting Australian flat oyster Ostrea angasi Sowerby

Sperm quantification is vitally important when sperm concentration is required for standardization of different fertilization treatments in a hatchery. Although the haemocytometer method is generally used to determine sperm concentration, the procedure is tedious and the attributes are not suitable for handling a large number of sperm samples within a short period. In this study, the efficiency of sperm concentration determination was improved in the spermcasting oyster Ostrea angasi Sowerby by optimizing the regression model and parameters critical to spectrophotometric reading. Although sperm concentration can be estimated in a wide range of wavelengths, the 350-nm wavelength produced the best fit to the regression model (y = 1 × 10⁻⁸ x + 0.163; r² = 0.996). In addition, the sperm counts estimated with this model were similar to the haemocytometer counts. The reading repeatability of this technique was further validated with samples from different individuals. Comparisons with literature suggest that when the spectrophotometric technique is applied to a new species for estimating sperm concentration, the regression relationship between sperm concentration and wavelength reading should be reassessed due to species-specific discrepancy.