CRYOPRESERVATION OF EUROPEAN CATFISH (SILURUS-GLANIS L) SPERMATOZOA

Semen of European catfish stripped into an immobilizing solution (200 mM NaCl, 30 mM Tris, pH 7) was successfully cryopreserved after a stepwise freezing and fast-thawing procedure. Drops of sperm were diluted in an immobilizing solution containing 12 or 15% of glycerol, held on aluminium discs and exposed for 10 min to liquid nitrogen vapour ( - 80 to - 85-degrees-C) before transfer into liquid nitrogen. Pellets were thawed for 20 s in test tubes (temperature 36-degrees-C). The survival of spermatozoa after thawing was evaluated from the total motility, the percentage of motile cells and the percentage of fertilization. Batches of 40-80 eggs in triplicate from several females were fertilized with cryopreserved/thawed spermatozoa activated with distilled water, this resulted in an average of 45.2% (range 4-48%) of hatched eggs compared to 70.6% (range 7-71%) with the intact sperm, using comparable numbers of spermatozoa/egg in both groups. In one experiment the percentage of hatched eggs was similar after fertilization with frozen and intact sperm. There was a relatively higher number of abnormal embryos in the frozen sperm group (52.5%, s.d. = 11.4%) in comparison with the control (31.5%, s.d. = 3.3%). However, this difference was not statistically significant. The motility of frozen sperm was slightly lower than that of the controls.