LAUSR

Abstract Northern pike (Esox lucius) sperm equilibration and cryopreservation were conducted using a simple cryopreservation extender (CE) containing 185 mM trehalose, 40 mM KCl, 20 mM Tris at pH 8.5 and supplemented with 10% of methanol. Sperm was diluted tenfold (1:9; sperm:CE), and a subset of the samples was equilibrated (over 15 min) and stored on crushed ice (+4 °C). The remainder of the samples were drawn into French straws of 250 μl capacity and subsequently frozen. Thawing of sperm was carried out in a hot water bath at 40 °C for five seconds. The control group was fresh sperm that was neither diluted in CE nor frozen. After equilibration and cryopreservation, sperm motility parameters were analyzed using a Computer-Assisted Sperm Analysis system. Fertilization using different sperm:egg ratios (i.e. 400, 200, 100, 50, 25 and 10 thousand sperm per egg) was performed to determine the fertilization capacity of sperm. Sperm motility parameters of northern pike remain at the same level in fresh, equilibrated and cryopreserved samples. On the other hand, average sperm longevity was longest in equilibrated (118.0 s.) and cryopreserved (124.5 s.) sperm in comparison to fresh sperm (84.7 s.). Sperm samples equilibrated in CE achieved higher (n = 4. P