Morphological approaches as tools to study the development of male germ cells of Crassostrea gasar (Mollusca, Bivalvia)

Crassostrea gasar is a bivalve mollusk of economic interest in the Amazon estuary, because it displays good zootechnical performance and nutritional value. However, there is still a gap in the literature regarding studies on basic biology, especially spermatogenesis at the ultrastructural level. This study aimed to describe for the first time the male gonad development. Gonad fragments were analyzed using light microscopy and transmission and scanning electron microscopy. The ultrastructural analysis of the gonadal tubule showed two distinct cell populations: support cells and the cells of the spermatogenic lineage. Regarding the ultrastructural aspects, support cells were characterized by an irregular shape, sparse electron-dense cytoplasm, and a large nucleus with condensed chromatin; and two types of spermatogonia were seen (A and B); spermatocytes I where it was possible to characterize four stages of prophase I, namely leptotene, zygotene, pachytene, diplotene; spermatocytes II showing a reduction in cytoplasmic and condensed chromatin. Spermatids were classified into three stages of development: early, middle, and late. Mature spermatozoa are of the primitive type and have a cone-shaped head with a discoidal acrosome, a midpiece formed by four mitochondria, and a long flagellum. This information can help establish phylogenetic relationships between species of the genus Crassostrea. In addition, these findings can support conservation biology by developing and implementing biotechnological approaches, such as cryopreservation, and contributing to commercial-scale cultivation in the Amazon region.

Graphical Abstract