The effect of egg yolk, low density lipoproteins, methylxanthines and fertilization diluent on cryopreservation efficiency of northern pike (Esox lucius) spermatozoa

The effect of egg yolk, low density lipoproteins (LDL) as well as methylxanthines (caffeine and theophylline) and fertilization diluent on cryopreservation efficiency of northern pike, Esox lucius, spermatozoa was tested. Milt was cryopreserved in pellets on dry ice then stored in liquid nitrogen. The extender consisted of 0.6 M sucrose + 15% DMSO supplemented with egg yolk or LDL fractions. The most effective results (77.3% hatched larvae vs 74.1% in the control group) were obtained from extender that contained only 0.6 M sucrose + 15% DMSO and was used for freezing, while the fertilization diluent was used for thawing. Addition of egg yolk or LDL to the extender did not improve the results. The presence of caffeine in the thawing solution significantly lowered fertilization rate of cryopreserved spermatozoa, whereas theophylline did not significantly affect the results. The addition of fertilization diluent to the eggs prior to insemination was superior to the other treatments. The proposed procedure constitutes a complete method for the efficient cryopreservation of northern pike semen.