Activity of aspartate aminotransferase and acid phosphatase in cryopreserved trout sperm.

Milt of brown, rainbow and brook trout was cryopreserved. Activity of aspartate aminotransferase (AspAT) and acid phosphatase was assayed both in supernatants and in spermatozoa obtained from thawed sperm samples; additionally, post-thaw motility was evaluated. Enzyme activities differed according to fish species and were strongly affected by the type of cryoprotectant used. The activity in supernatants was usually higher than that in spermatozoa because of protein leakage from injured cells. AspAT activity in cryopreserved spermatozoa correlated positively with fertilization success in all three species. There was a negative correlation between activity of extracellular (supernatant) AspAT and fertilization rates in variants with dimethyl sulfoxide and dimethylacetamide-based extenders. The motility of thawed sperm, determined microscopically, provided some information on the cryopreservation efficiency of trout milt.