Relationships among morphological status, steroid hormones, and post-thawing viability of frozen spermatozoa of male minke whales (Balaenoptera acutorostrata)

Spermatozoa from 21 mature minke whales (Balaenoptera acutorostrata) taken in the Antarctic Ocean for Japanese research were recovered from vasa deferentia, diluted 1:9 in a Tris-based diluent, and frozen at -80 degrees C on board the vessel. After a period ranging from 45 to 125 d, the samples were transferred to liquid nitrogen and transported to the laboratory. After thawing at 37 degrees C, the motility (percentage of motile spermatozoa), vitality (proportion of live spermatozoa), and sperm concentration were determined for each sample. These values were tested for correlations with morphological measurements (body size, body weight, testis weight) and serum concentrations of progesterone (P-4), estradiol-17 beta (E(2)), and testosterone (T). Ten of 21 samples had motile spermatozoa (2%-40%). Although no motile spermatozoa were observed in 11 samples, all sperm samples were examined by eosin-nigrosin staining and showed vitality levels of 3%-44%. It was found that the motility (r = 0.54) and vitality (r = 0.53) of the spermatozoa were significantly (P < 0.01) correlated with the E(2) levels (8.50 +/- 1.80 pg/ml). Serum T levels (0.07 +/- 0.02 ng/ml) were significantly correlated with the E(2) levels (r = 0.58, P < 0.01), but sperm concentrations were not correlated with either E(2) Or T levels. The present study demonstrates that spermatozoa of minke whales can be successfully cryopreserved.