Common carp (Cyprinus carpio) sperm reduction during short-term in vitro storage at 4 °C

This study was designed to optimize a short-term storage protocol for common carp sperm at 4 °C under aerobic condition. Sperm from individual males were collected directly with or without extenders. The results demonstrated that in general, it was similar effect to collect sperm directly in extenders and keeping sperm for 0.5 h after collection without extenders. Sperm was diluted with eight selected extenders (sperm: extender = 2:1, 1:1 and 1:9) and undiluted sperm was used as a control. Sperm and seminal plasma parameters (sperm motility, velocity, membrane integrity, sperm concentration, osmolality and pH in seminal plasma) were evaluated in sperm stored on ice under aerobic conditions at 0, 2, 4, 6 and 8 days post stripping (DPS) using the computer- assisted sperm analysis system. Results showed that 1:1 and 2:1 dilution maintained higher sperm function and more sperm for a longer period. After 8 DPS, the best sperm quality and quantity was recorded in the common carp seminal plasma supplemented with 50 mM NaCl, Cejko extender (2 mM CaCl₂, 1 mM MgSO₄, 20 mM Tris, 110 mM NaCl, 40 mM KCl, pH 7.5 and 310 mOsm/kg) supplemented with/without 25 mM KCl/NaCl. The reduction of spermatozoa number with time during short-term storage but varied according to different dilution ratios and extenders. At 8 DPS, sperm count has dropped by 22.9 % in a dilution of 1:1 compared to 50.3 % in sperm without dilution. Extenders with diluted 1:1, especially Cejko solution, largely postponed sperm reduction, 21.3 % compared to 55.5 % for sperm stored without extenders.