Ecología reproductiva de tres batoideos (Chondrichthyes): iAtlantoraja castelnaui (Rajidae), Rioraja agassizi (Rajidae) y Zapteryx brevirostris (Rhinobatidae). Implicancias de distintas estrategias reproductivas en un escenario de explotación comercial intensiva
The reproductive ecology of the Chondrichthyans Atlantoraja castelnaui (spotback skate), Rioraja agassizi (rio skate) and iZapteryx brevirostris (lesser guitarfish) is analyzed in this study. The two first are oviparous species that attain 168 mm and 768 mm of maximum total length (MTL), respectively. The third is a viviparous lecitotrophic ray that grows to a MTL of 720 mm. The examined material came from the purchase of samples in the Mar del Plata Port (Buenos Aires prov., Argentina) and from research cruises carried out by the National Institute of Fisheries Research and Development (INIDEP). Two work lines were developed to analyze the reproductive ecology and to validate the reproductive stages of these species, one based on macroscopic analysis of reproductive organs and another based on histological study of the reproductive organs. In A. castelnaui, the length at witch the 50% of the individuals attain the sexual maturity (TL50) was estimated at 980 mm TL for males and at 1089 mm TL for females; the TL50 for iA. castelnaui was estimated at 1038 mm TL (78,4% of MTL). In R. agassizi, the TL50 was estimated at 479 mm TL for males and at 547 for females; the TL50 for this species was estimated at 496 mm TL (74% of the MTL). Sexual dimorphism in maximum size and size at maturity was observed, with females larger and maturing at a larger size than males. This dimorphism, common in viviparous Chondrichthyans, is quite variable in oviparous. The TL50 in Z. brevirostris was estimated at 499 mm TL for males and at 505 mm TL for females; the TL50 for this species was 502 mm TL (74% of the MTL). The lack of correlation between TL and the number and size of embryos, could be explains the absence of sexual dimorphism in MTL and TL50. The skates R. agassizi and A. castelnaui shows an annual reproductive cycle, with a peak in reproductive activity. This conclusion is based on the seasonal variation of the ovaries, oviducal glands and the presence of egg-laying females throughout the year. Sperm storage was observed in oviducal glands of A. castelnaui and R. agassizi, but unlike other skates, it was observed in the serous lobule. A. castelnaui and R. agassizi males are capable of reproduction throughout the year. This conclusion is based on the analysis of testicles, mature cyst proportion and the presence of sperm in deferent ducts. Four stages are observed in mature females of Z. brevirostris: a) non pregnant with small ovarian follicles, b) non pregnant with big ovarian follicles, c) pregnant but no embryos distinguished and d) pregnant with embryos differentiated. The reproductive cycle of females takes three years, with two years of ovarian development (stages a and b) and one year of gestation (stages c and d). Ovulation, birth and mating take place during winter months. In males three patterns of reproductive activity are observed: in spring the testicles are conformed by immature cysts and the ducts are empty; in summer and fall, mature cysts are increased and the ducts contains are small quantities of sperm; in winter months, the cysts are mature and the ducts are full of sperm in different aggregations stages. The winter condition confirms the capacity of sperm storage in males. The highest values of liver weight observed during summer and winter months suggest that the peaks in energy storage take place before the mating season. The vulnerability of analyzed species and the abundances trends, denote the necessity to intensify the studies that allow evaluate population dynamics for the conservation of these species.