CRYOPRESERVATION OF COMMON CARP (CYPRINUS-CARPIO L) SPERM .2. OPTIMALCONDITIONS FOR FERTILIZATION

Experiments were carried out on the cryopreservation of common carp (C yprinus carpio L.) sperm. Optimal conditions for fertilization includi ng suitable medium and sperm:egg ratio were determined. Sperm was dilu ted in modified Kurokura's 'Extender 2' containing DMSO as cyroprotect ant in 10% final concentration. The dilution rate was 1:9 (sperm:dilue nt). Sperm was diluted and equilibrated (10 min) at 2 degrees C. Sperm was then frozen in plastic straws (0.5 ml) at the following rate: 0 d egrees C--4 degrees C: 4 degrees C min(-1); -4 degrees C--80 degrees C : 11 degrees C min(-1) from -80 degrees C they were plunged directly i nto liquid nitrogen (- 196 degrees C). Frozen samples were thawed in a water bath at 40 degrees C. Fertilization rates achieved were much hi gher in water than in other solutions. Optimal ratios of frozen sperm: egg:water (1:20:20 in volume) and optimal number of frozen spermatozoa :egg (10(5) spz: 1 egg) were determined. In such conditions, a strong positive correlation (c = +0.846) was found between the post-thaw moti lity and the fertility of frozen sperm securing high fertilization (99 .6%, percent of control). No significant difference was found between fertilization and hatching rates achieved using frozen-thawed common c arp sperm.