The percentage of sperm motility (92-100%), spermatozoan velocity (112-163 microm.s(-1)) and control hatching rates (83-96%) were evaluated for each of six gold and five green male common carp (Cyprinus carpio). In all 30 possible paired combinations of sperm-competition tests, hatching rates of 90-97% were achieved. The mean percentage of offspring sired was strongly influenced by the male used (P < 0.001, R2 = 0.91). The best male sired an average of 88% of the offspring in its competition tests, and the worst male sired only 5%. Spermatozoan-quality parameters could explain only part of the variation in male competitive ability. The male effects alone explained 91.4% of the observed variance, consisting of 17.1% explained by spermatozoan motility and 32.5% by control hatching rates in single fertilizations. Undetermined male effects explained 41.8%. The velocity of spermatozoa had no effect on the outcome of sperm competition. Neither was there any link between spermatozoan velocity and hatching rate in a control hatching test, whereas there was an effect of motility on hatching rate in this same test.

Joint Laboratory of Genetics Physiology and Reproduction of Fish University of South Bohemia Research Institute of Fish Culture and Hydrobiology 38925 Vodnany Czech Republic