Ultrastructure of carp Cyprinus carpio spermatozoa after cooling, dilution and freeze-thawing

Dilution of the carp spermatozoa with a cryoprotective medium was shown to inflict serious injuries to the fine structures of some spermatozoa. The amount of the injured spermatozoa increases after cryopreservation. Examination of the freeze-fracture micrographs of the heads of the carp spermatozoa, showed that their protoplasmic faces were covered with the particles in high concentrations. These particles do not form clusters after cooling the spermatozoa down to +5°C and dilution with a cryoprotective medium. For the first time the authors observed the particles to form geometrically shaped regular formations on the outer membranes of the carp spermatozoa.

On the basis of the results obtained the authors propose that high susceptibility of the carp spermatozoa to osmotic exposures is apparently due to some particular features of the fine structures of their membranes and to their expected probably low heterogeneity.