Ultrastructural investigations on spermatogenesis and spermatozoan morphology in the endangered Adriatic sturgeon, Acipenser naccarii (Chondrostei, Acipenseriformes)

Abstract

Spermatogenesis was investigated in the Adriatic sturgeon, Acipenser naccarii, by light and electron microscopy. The testis of the unrestricted type had a germinal compartment composed of lobules containing germ cells and Sertoli cells, and separated by a basal lamina from the interstitial compartment, in which Leydig and myoid cells were detected for the first time in Acipenseridae. Spermatogenesis occurred in spermatocysts produced when Sertoli cells became associated with type A spermatogonia of subsequent generations, which produced a clone of synchronized aligned spermatogonia. In primary spermatocytes at zygo-pachytene stage, the large spherical nucleus contained synaptonemal complexes. The smaller secondary spermatocytes were ovoid with a central round nucleus and scarce cytoplasm. Spermatids were interconnected by cytoplasmic bridges until early spermiogenesis. Chromatin initially condensed as long, twisted, and nonhomogeneous fibers and finally as a compact structure made of thick filaments.Early spermatids showed the flagellum, the primordia of centriole complex and of "implantation fossa," followed by the acrosomal vesicle formed by Golgi complexes and a fibrous body associated to centriole complex. The spermatozoan head had 10 postero-lateral projections and a trapezoidal nucleus, a cylindrical midpiece with six to eight mitochondria, the centriole complex, and a "9 + 2" flagellum with a pair of lateral fins. Three helical endonuclear canals crossed the nucleus from the acrosome base to the implantation fossa; their spiralization and that of chromatin fibers suggest a spiral twisting of the nucleus during spermiogenesis. The Sertoli cells performed phagocytosis of degenerating spermatids and spermatozoa. Significant interindividual differences were detected in most morphological parameters of spermatozoa. Data on spermatogenesis in A. naccarii and morphometric measurements on mature spermatozoa provide information about the reproductive biology of the species useful not only for phylogenetic studies but also for evaluation of sperm quality for artificial reproduction projects and restocking of this and other critically endangered sturgeon species. K E Y W O R D S Acipenseridae, Sertoli cells, spermatozoon, testis, transmission electron microscopy

A Deep Insight of Spermatogenesis and Hormone Levels of Aqua-Cultured Turbot (Scophthalmus maximus)

“…And it corresponded to the stage of Spermatid II in the present study. A recent study on Adriatic sturgeon (Acipenser naccarii) also showed that the flagellum occurred in early spermatids, although spermiogenesis was not clearly divided (Grandi et al, 2018).…”

Early gonadal maturation and vitellogenin mRNA expression in Siberian sturgeon Acipenser baerii cultured in a semi-closed water recirculating system in Korea

“…Siberian sturgeon males in this study is potentially capable of the final maturation of male gametes at the age of 4 years. Although not all those males were tested, several 4-year-old males subjected to induced hormonal spermiation trials were proven to be able to provide a good quality of sperm that can be highly compatible with artificial insemination trials (data not shown), suggesting that, at least in a certain portion of males, the process of not only spermatogenesis but also functional spermiogenesis could be completed by this age (Schulz et al, 2010;Dzyuba et al, 2017;Grandi et al, 2018).…”