Changes in motility, ultrastructure, and fertilization capacity of striped bass Morone saxatilis spermatozoa following cryopreservation

Abstract

In the present study, motility, ultrastructure and fertilization capacity of fresh and cryopreserved striped bass spermatozoa were investigated in order to evaluate semen dilution ratio, freezing rate and cryomedia. Four dilution ratios (semen/cryomedia), and four freezing rates were evaluated on the basis of post-thaw sperm motility. The dilution ratio of 1:3 yielded the highest ( P<0.05) post-thaw motility. Sperm cryopreserved with a freezing rate of −40°C min −1 resulted in a higher percentage of motile sperm ( P<0.05) than other lower freezing rates we examined. Six cryomedia with various dimethyl sulfoxide (DMSO) and glycine concentrations were tested for their influences on ultrastructure, post-thaw motility and fertilizing capacity of cryopreserved sperm. The ultrastructural results revealed that the plasma membranes of spermatozoa were better protected with the higher DMSO concentrations we examined. Two cryomedia containing 5% or 7.5% DMSO, both with glycine added, resulted in the highest ( P<0.05) post-thaw motility compared with other cryomedia without glycine. The percentage of eggs fertilized with sperm cryopreserved in six cryomedia ranged from 26±2.1% (2.5% DMSO without glycine) to 54±5.6% (7.5% DMSO with glycine), which were equivalent to 44% and 90% of fresh semen controls. No differences ( P>0.05) were detected in the percentage of eggs fertilized among DMSO concentrations that did not contain glycine, although post-thaw motility did vary significantly ( P<0.05) in these treatments. These results suggest that adding glycine to our basic cryomedia containing DMSO increases the fertilization capacity of these cryopreserved spermatozoa.