Reproduction and its seasonal variation in the soupfin shark, Galeorhinus galeus

[摘要] ENGLISH ABSTRACT:The soupfin shark, Galeorhinus galeus, is a circum-global shark species of great economicalimportance. Their reproductive biology is reasonably well understood, but intraspecificdifferences between global populations necessitate the study o f populations separately. Forthis study, 70 male and 74 female specimens were collected along the southwestern coast ofSouth Africa between 34°8'S; 18°27'E and 34°24S; 21°25'E. Morphological changes weredescribed and serum steroid hormone concentrations evaluated by enzyme-linkedimmunosorbent assay (ELISA) over an almost-complete reproductive cycle. Males display anannual spermatogenic cycle that starts with a significant peak in testosterone concentrationscoinciding with the start o f spermatogenesis around April-May. Testosterone levels decreaseto reach a minimum in late-winter after which spermiogenesis commences. The prevalence ofspermiogenic cysts in the testis increase to reach a peak between February and April, afterwhich mating occurs until about July. Females (aplacentally viviparous) are suggested tohave a triennial cycle, similar to the Brazilian & Australian populations, but different from theCalifornian & Mediterranean populations. During the first year after parturition there is notmuch reproductive development. The following year sees increased vitellogenic activity inovarian follicles and development of the oviducal glands and uteri. Ovulation then occurstowards the end of that year. Mating is suggested to precede ovulation by two to three monthsnecessitating sperm storage by the females in their oviducal glands. A 12-15 month gestationensues and ends in parturition the following summer. Testosterone and estradiol levelsfluctuate together and are involved in the preparation for ovulation and oviducal glanddevelopment. Progesterone levels show two distinct peaks during the year, in both immatureand mature females, and could not yet be functionally linked to any reproductive activity orcondition. This cycle is not very tightly synchronised among the South African females.

[发布机构] Stellenbosch University