Elevated temperature promotes spermatozoa motility kinetics and fertilizing ability following short-term storage: An implication for artificial reproduction of common carp Cyprinus carpio in a hatchery

Abstract

Short-term storage of sperm in an extender at a low temperature has been widely applied in hatchery management. In the present study, for the first time, we examined the effects of elevating temperature on spermatozoa motility kinetics and fertilization ability after short-term storage at 0–2 °C. Sperm of common carp (Cyprinus carpio L.) was diluted with an extender (110 mM NaCl, 40 mM KCl, 2 mM CaCl2, 1 mM MgSO4, 20 mM Tris, pH 7.5, 310 mOsmol/kg) at the ratio 1:1 (v/v) in containers and stored for 6–9 days at 0–2 °C under aerobic conditions. At the end of storage, the sperm suspension was incubated at 20 °C for >10 min and spermatozoa motility, velocity [straight-line velocity (VSL) and curvilinear velocity (VCL)], viability, and fertilizing ability were recorded. Spermatozoa motility of sperm stored for 6 days was significantly increased after incubation at 20 °C for 10 and 20 min and activation in both distilled water and a saline solution (45 mM NaCl, 5 mM KCl, 30 mM Tris, pH 8.0). Elevating the temperature did not affect spermatozoa viability. Spermatozoa motility, VSL and VCL, and viability were decreased at 3 days post storage (DPS) after activation in distilled water without incubation at 20 °C. However, elevating the temperature for 10–20 min at any time post sperm storage (3, 6 or 9 DPS) could promote spermatozoa motility kinetics. For sperm stored for 9 days, fertilization and hatching rates were increased when it was incubated at 20 °C for 10 and 20 min prior to fertilization at the ratio 30,000 spermatozoa per egg. Increasing the spermatozoa to egg ratio to 100,000:1, however, masked the temperature effects on fertilization and hatching rates. Finally, a large-scale experiment was performed in hatchery in which sperm stored for 8 days was incubated for 2 h at 20 °C, resulting also in an increase in spermatozoa motility and fertilizing ability. Results of the present study show that elevating the temperature following short-term storage of common carp sperm at low temperatures improved spermatozoa motility kinetics and their fertilizing ability. This method may contribute to developing artificial reproduction of economically important fish species in aquaculture.