Sperm motility and cryopreservation of spermatozoa in freshwater gobies

Abstract

Testicular sperm motility and methods for the cryopreservation of spermatozoa in the freshwater goby Rhinogobius sp. CB (Cross Band type) were examined. Spermatozoa were almost immotile upon dilution with 300 mOsm kg−1 of NaCl, KCl and mannitol solutions but began to swim in solutions with concentrations <200 mOsm kg−1. The highest percentage and longest duration of motility was obtained in the 0 and 100–200 mOsm kg−1 solutions, respectively. The highest post‐thaw motility, c. 50% of motility before cryopreservation, was obtained when spermatozoa were diluted with an extender of 10% methanol and 90% artificial seminal plasma, cooled at −10·0 ± 1·1° C min−1 (mean ±s.e.) to −50° C and plunged into liquid nitrogen. Spermatozoa were cryopreserved in a 50 μl acrylic haematocrit tube to store the small amount of milt. As the cryopreservation method described above was applicable to the endangered Rhinogobius sp. BI (Bonin Island type), it is probable that this method can be used for other species of freshwater gobies.