Ovarian follicular development in the hawksbill turtle (Cheloniidae: Eretmochelys imbricata L.)

Abstract

Ovarian follicular development is an essential process in the determination of maturation stages associated with size. This association acquires importance when managing populations of threatened species. We histologically processed 11 prepubescent ovaries, four pubescent ovaries, and one breeding adult ovary with vitellogenic follicles using specific staining techniques to identify the follicular stages of Eretmochelys imbricata. Follicular stages were compared with maturation stages [including straight carapace length (SCL)]. The ovary presented several germinal beds and a lacunar system less histochemically and morphologically heterogeneous than that of crocodiles. During previtellogenesis (four stages), the oocyte grows rapidly due to the strong transcriptional activity of lampbrush chromosomes and numerous nucleoli, and the strong metabolism associated with lipid synthesis. The Stage III ooplasm showed a Sudan positive band. This stage was the most frequent in all ovarian sections and it was independent of maximal follicular stage. Stage IV, more frequent in pubescent and adult ovaries, presented a lipid vacuole-rich ooplasm and a broadening of the zona pellucida and the theca. The vitellogenesis begins with the penetration and accumulation of spherical glycoprotein yolk platelets and chemically neutral lipid droplets which are observed to be mixed, but spatially and chemically segregated. Both the yolk platelets and lipid droplets increase in size, density, and proximity to the periphery of the oocyte due to their coalescence. The SCL of the immature females did not determine the maximal follicular stage nor its frequency in the ovaries. Straight carapace length turned out to be an imprecise measure in identifying the presence of follicular stages in females larger than the minimum legal size limit in Cuba. Consequently, for a national conservation program to be successful, it must emphasize the critically endangered status of E. imbricata, as well as the maturity of the most frequent hawksbill sizes encountered in the Cuban archipelago fishery.