Common Carp Spermatozoa Performance is Significantly Affected by Ovarian Fluid

During evolution, the fish adopted versatile spawning tactics, which allowed them to use sperm competition effectively and prevent fertilization by inappropriate male gametes. Ovarian fluid (OF) affects spermatozoa performance in several fish species, as shown mainly in salmonids, and likely contributes to their reproductive tactics. Common carps utilize different spawning behavior compared to salmonids, which is accompanied by specific interactions of male gametes and maternal fluids, as observed in this study. The presence of common carp OF in the activation medium caused the decrease of spermatozoa velocity and altered the motility pattern from straightforward motility observed in the water to the hyperactivation-like tumbling in a swimming medium complemented by 50% OF. The chemotactic test (microcapillary sperm accumulation test) showed a significant response of carp spermatozoa to the OF. The attraction phenomenon depended on the presence of external calcium ions: the spermatozoa lost the ability to react to the attractant if the Ca2+ was absent in the activating medium. The carp spermatozoa were responsive to “osmotaxis”. Thus, the environmental conditions that accompany the encounter of gametes, particularly the presence of OF, significantly affect the performance of male gametes in common carp, which is in line with their spawning behavior.