MOTILITY AND FERTILIZING-CAPACITY OF FRESH AND FROZEN-THAWED SPERMATOZOA IN STURGEONS ACIPENSER BAERI AND A-RUTHENUS

The Siberian sturgeon (Acipenser baeri) and the sterlet (A. ruthenus) were injected with dried sturgeon pituitary (2 mg kg(-1)), yielding 24 h later respectively 1.71+/-0.5 and 1.65+/-0.5 10(11) spermatozoa kg( -1) body weight. Spermatozoa were best activated with a solution of Tr is HCl 50 mM, pH 8.0. The percentage of activated cells was 88+/-4.4 i n A. baeri (n = 5) and 68+/-19 in A. ruthenus. (n = 5). In A. baeri, i mmediately after activation, the beat frequency of the flagellum and t he mean velocity were in the range of 48-52 Hz and 100-300 mu m(-1) s, respectively. The beat frequency declined to 15 Hz at 30-40 and veloc ity to 100 mu m s(-1) at 60 s post-activation. Only a small percentage of the spermatozoa remained motile after 3-4 min. In all cases sperma tozoa showed mostly quasi-linear trajectories. Sperm was frozen in liq uid nitrogen vapor immediately after dilution 1 v: 1 v in a cryopreser vation medium (23.4 mM saccharose, 118 mM Tris-HCl pH 8.0, 20% egg yol k to which 15% DMSO were added). After fast-thawing procedure (25 s at 40 degrees C), the percentage of motile spermatozoa (once activated i n 118 mM Tris-HCl, pH 8.0) decreased to 23+/-8.8 in A. baeri and to 15 +/-11 in A. ruthenus. The fertilizing capacity also decreased: 53+/-8. 3% vs. 89+/-7.6% in control (P < 0.05) in A. baeri and 23+/-11% vs 53/-8.3% in control (P < 0.05) in A. ruthenus. The motility pattern of t he surviving frozen/thawed spermatozoa was the same as in fresh sperma tozoa.