EFFECT OF CRYOPRESERVATION ON THE FINE-STRUCTURE OF SPERMATOZOA OF RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) AND BROWN TROUT (SALMO-TRUTTA F FARIO)

Freeze-fracture electron microscopy has revealed that changes are indu ced in the organization of the plasma membranes of spermatozoa of rain bow and brown trout when they are cryopreserved. Electron-micrographic images of spermatozoa that had nor been exposed to cryopreservation s howed a protoplasmic surface with particles homogeneously distributed. The concentration of the particles was low. In the median portion of the tail the authors observed longitudinal strips, consisting of parti cles located along the bands. In the neck of the spermatozoon the part icles were aggregated in a chaotic manner. Electron micrographs of tro ut spermatozoa that had been cryopreserved showed particles grouped in rounded clusters on the protoplasmic surfaces of both the head and th e tail. In some spermatozoa, folding of the protoplasmic membrane, wit h the particle-free sites, were found. The dimensions of the clusters and the spaces that were free of particles suggest that, after thawing , the spermatozoa of the brown trout is likely to experience greater d ifficulty in restoring their physiological integrity than those of the rainbow trout. These results suggest that the membrane proteins of sp ermatozoa of the species of trout that were studied possess high motil ity and diffuse, with the formation of clusters, in very short periods of time (about 30 s). The changes in membrane structure of the trout spermatozoa following cryopreservation appear to indicate high labilit y. (C) 1998 Academic Press.