Sperm biology of Merluccius australis: Sperm structure, semen characteristics and effects of pH, temperature and osmolality on sperm motility

In this article we describe basic aspects of the sperm biology of Merluccius australis, in particular assessing the effects of pH (6, 8 and 10), temperature (4, 10 and 15 °C) and osmolality (922 mOsm/kg, 822 mOsm/kg, 681 mOsm/kg and 3 mOsm/kg) on sperm motility. Our results indicate the presence of semen with sperm density of 4.6 × 109 sp/ml which contains a primitive spermatozoon with total length 40.95 ± 1.5 μm, with no acrosomes and two mitochondria. Sperm motility is initiated on contact with a hyperosmotic swimming medium (SM), and under normal conditions (922 mOsm/kg, pH 8 and 14-15 °C) may last for up to 9.18 min; however a pH higher or lower than 8 has a negative effect on both motility and the percentage of motile cells (%MC). The longest motility period (696 s) was recorded at 4 °C; however, regardless of the temperatures assessed, a gradual decrease in motility was observed as the osmolality of the SM diminished, with immobility observed at 3 mOsm/kg. The information generated in this research will be useful for developing biotechnology tools for the effective management of M. australis gametes.