Ultrastructure of the Spermatozoa of the Yangtze Finless Porpoise (Neophocaena phocaenoides asiaeorientalis)

Semen sample was collected from two captive adult Yangtze finless porpoises (Neophocaena phocaenoides asiaeorientalis) during physical examination. One individual was aged about 9 years with body length 143 cm (total length) and body weight 46.1 kg in 2003. The age of the other was unknown and its body length was 147 cm and body weight was 43 kg in 2004. Ultrastructure of their spermatozoa was examined using scanning and transmission electron microscope. The sperm concentration was 4.17 x 10(9) spermatozoa per ml by the cytometer. The approximate dimensions of the spermatozoa were as follows: head length, 3.366 +/- 0.140 microm (mean +/- SE, n = 15); head width, 1.896 +/- 0.099 microm (n = 15); and neck length, 1.004 +/- 0.074 microm (n = 10). The tail included midpiece, principal piece and terminal piece. The length of the midpiece was 1.882 +/- 0.077 microm (n = 9). There is no apparent boundary between the principal piece and the terminal piece, so the length of the principal piece and the terminal piece was 44.612 +/- 3.485 microm (n = 5). Total length of the spermatozoa was 53.314 +/- 4.580 microm (n = 10). The acrosome covered approximately 45.8% of the anterior portion of the head.