A study of reproductive physiology in the male ocean pout Macrozoarces americanus

Wang, Zhilan (1996) A study of reproductive physiology in the male ocean pout Macrozoarces americanus. Masters thesis, Memorial University of Newfoundland.

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Abstract

To provide more information on the reproductive biology of an internally fertilizing marine species, a two-year study of the reproductive physiology of the male ocean pout (Macrozoarces americanus) was undertaken. The physiological characteristics of the spawning season and sperm physiology, including the changes in the gonadosomatic index (GSI), plasma androgenic steroids, the timing of spermiation, sperm motility and sperm concentration, and the variations of pH, osmotic pressure and the biochemical composition of seminal plasma during the spawning season were investigated. The spermiation response began in June, and by July all mature males spermiated. Spermiation ended in late September or early October. Sperm motility rose and fell in a similar manner from June to September. Compared with the milt of most investigated male teleosts, ocean pout milt had a low sperm concentration (0.91 - 6.81 x 10⁸ spz/ml), and was correlated with spermatocrit values during most of the spawning season (r²-0.79, p<0.0001). The GSI of the males was relatively low, ranging between minimum values in September and October (0.26 - 0.31%) and a maximum in July (1.9%). Plasma testosterone levels rose rapidly seven weeks in advance of spermiation and peaked one week before the onset of spermiation, and decreased thereafter. Plasma levels of 11- ketotestosterone paralleled those of testosterone during the spawning season and reached a peak coincident with onset of spermiation. -- Biochemical composition of seminal plasma also varied through the spawning season. The pH of seminal plasma increased from 7.4 to 7.9 during the period of spermiation, and the average pH (7.78±0.03) for the spawning season remained close to an experimentally determined optimum pH range for ocean pout sperm motility (pH 8-9). Although the values for seminal plasma osmolality fell from 416 to 339 mmol/kg during the reproductive season, the average osmolality value (356±3 mmol/kg) was within the optimum for ocean pout sperm motility (300 - 400 mmol/kg). In comparing fluctuations in sperm motility with the biochemical composition of ocean pout seminal plasma during the spawning season, this study showed that increased Mg levels were correlated with the summer period of maximum sperm motility. A seasonal decline in Na and Cl ion levels was reflected in lower seminal plasma osmolality values.

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