Abstract
This work aims to study the female reproductive tract of silky sharks, Carcharhinus falciformis, captured in the South and Equatorial Atlantic Ocean. Samples were collected between January 2008 and March 2010 through oceanic commercial vessels that targeted tuna and swordfish, with a total of 17 females collected. The methodologies followed for analyzing the ovaries of those females included both macroscopic and histological analysis. Macroscopically, it was possible to determine that the ovaries on these sharks is suspended by mesenteries in the anterior section of the body cavity, heavily irrigated by blood vessels, and contains a wide range of oocytes. Ovaries were found in three distinct maturational stages: Stage I (Immature), Stage II (Maturing) and Stage III (Mature). Immature ovaries were small, with widths ranging from 1.0 to 3.1 cm, and had a gelatinous or granulose internal structure; maturing ovaries were slightly larger, ranging in width between 5.2 and 6.0 cm; mature ovaries ranged in width between 6.5 and 7.8 cm, and had a more rounded shape and the presence of large and well developed oocytes. Under microscopic examination, it was observed that the ovaries were covered with simple epithelial tissue during the early development stages and a simple cubic epithelium in the final stages of maturation. During the initial maturation stages the epigonal organ was not differentiated from the ovary. In mature specimens, the ovary showed a simple cubic epithelium and just below this epithelium there was a layer of dense connective tissue and muscle with the presence of vitellogenic oocytes and fat cells. A thin yolk membrane enclosing the oocytes was also evident. Finally, it was possible to distinguish a zona pellucida, separating the oocytes from the follicle wall and a basal lamina between the granular layers and the teak layer.
Highlights
Material and MethodsAll elasmobranch fishes share some reproductive characteristics such as external sexual dimorphism, internal fertilization, and existence of paired reproductive organs, apparent lack of parental care, low fertility rates, and delayed sexual maturity (Dood, 1983)
The aforementioned being considered, the aim of this study is to describe both macroscopically and microscopically the morphology of the female reproductive tract of the silky shark, Carcharhinus falciformis (Müller & Henle, 1839), the maturity stages of the ovaries
According to previous works by Dodd (1983), Hamlett et al (1999), Koob & Callard (1999), Carrier et al (2004) and Hamlett (2007), the ovaries of female sharks are arranged in pairs and suspended by mesenteries in the anterior section of the abdominal body cavity, in an analogous position to the males’ testicles
Summary
Material and MethodsAll elasmobranch fishes share some reproductive characteristics such as external sexual dimorphism, internal fertilization, and existence of paired reproductive organs, apparent lack of parental care, low fertility rates, and delayed sexual maturity (Dood, 1983). The pups are born at an already welldeveloped stage, with the early life stages of the pups taking place internally in the mother’s ovissac (womb). This strategy is present in 56% of all Chondrichthyan fishes. The most derived or “advanced” (placentotrophic and uterine) are known as matotrophic vivipary, where there is a higher degree of nutritional dependence from the embryos in relation to the mother In this mode, the embryos receive nutrients through the yolk sac, but once those nutrients are used, the sac surface comes into close contact with the uterine wall, and tissue of both the mother and the offspring grows in close contact forming the placenta. Once the placenta is formed, nutrients can be diverted to the embryo through the mother’s bloodstream (Carrier et al 2004)
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