Common carp (Cyprinus carpio Linneaus, 1758) male fertilization potency with secure number of spermatozoa per ova

Summary The objective of this study with common carp spermatozoa was to understand the fertilization potency of different males when different sperm quantities were applied per ova of a single female. The sperm of five males representing very good sperm motility and the ova from one female exhibiting the best apparent quality were used. The sperm of each male was collected at volumes of 5 (1000 spermatozoa), 10 (5000 spermatozoa), 20 (10 000 spermatozoa), 40 (20 000 spermatoza) and 400 μl (200 000 spermatozoa) and pre-diluted with 995, 990, 980, 960 and 600 μl of Kurokura solution, respectively. Thereafter, 4000 eggs and pre-diluted spermatozoa from each male, one by one, were simultaneously added to 1000, 5000, 10 000, 20 000 and 200 000 spermatozoa and activated with hatchery water. Initial sperm motility was in the range of 89.5–97.2% at 15 s, decreasing to 19.1–30.2% at 60 s post-activation. At all times of evaluated post-activation, the sperm motility did not differ significantly among the males. Sperm velocity decreased from 126.1 to 161.2 μm s−1 at 15 s to 11.9–35.2 μm s−1 at 60 s post-activation. Sperm velocity was significantly different among males at 15 s post-activation. Fertilization and hatching rates were similar in all males at a higher examined number of spermatozoa per ova (20 000 and 200 000). Similar fertilization and hatching rates were observed in four out of five males at 10 000 spermatozoa per ova. Lower spermatozoa per ova (5000) induced very different results, from 48 to 82% for fertilization rates and from 42 to 72% for hatching rates. At 1000 spermatozoa per ova a very high variability was observed: 10–50% for fertilization rates and 8–43% for hatching rates. These results did not correspond to sperm velocity among males. The 20 000 spermatozoa density was considered as providing a secure number of spermatozoa for reaching good fertilization in common carp. To avoid loss of genetic variability for future generations this recommendation is important to know for the management of hatcheries where these broodstocks will be generated.