Studies of the testicular tissue and spermatogenesis in the brown shrimp Penaeus aztecus (Decapoda)

The male reproductive system of the brown shrimp Penaeus aztecus consists of paired testes, vasa deferentia, ducts and ampoules. The testis is composed of five testicular lobes which empty into the vas deferens. The vas deferens terminates in a small duct which extends to the ampoule. The testis is surrounded by a cortex composed of a thin layer of fibrous connective tissue. Within each testicular lobe is a tightly coiled seminiferous tubule. The cortex of this tubule consists of a single layer of muscle cells resting on a basement membrane. Each seminiferous tubule is packed with spermatogenic and supportive cells. The supportive cells are irregularly shaped, and contain large polymorphic nuclei with aggregates of heterochromatin. Spermatogonia are large cells which contain centrally located nuclei and are always found around the periphery of the seminiferous tubule. Only one cell type other than spermatogonia is found at any particular time within a single wild caught male, i.e; spermatogenesis is synchronous. The primary spermatocyte contains a large centrally located nucleus with dispersed chromatin. Synaptonemal complexes are often observed in the nucleoplasm. The primary spermatocyte has a very distinct cytoplasm which contains large quantities of swollen dense cisternae, Golgi bodies and stacks of annulate lamellae. Large granular electron dense inclusions are often found closely associated with these lamellae. The secondary spermatocyte contains dispersed clumps of heterochromatin in the nucleus. Anastomosing reticular elements and chain-like mitochondria are prevalent in the cytoplasm. Synaptonemal complexes are also noted at the second meiotic prophase. During subsequent division stages, the endoplasmic reticulum becomes displaced around the periphery of the cell. The resultant cells of the second meiotic division are spermatids which undergo an elaborate period of differentiation resulting in the formation of mature sperm. The cytoplasm of spermatids in early stages contains vacuoles in various sizes. These vacuoles containing flocculent material eventually fuse together and form a distinct cap around one end of the cell. Subsequently, nuclear condensation and decondensation take place. The mature sperm can be divided into four components:(])the head; (2) the cap; (3) the base; and (4) the spike. The head is composed of a central nucleoid region containing deoxyribonucleic acid and surrounded by a cytoplasmic band. The cap fluoresced orange when vitally stain with acridine orange suggesting the presence of ribonucleic acid or acrosomal-like enzyme. The acrosomal nature of the cap is reinforced by the PAS-positive nature of this region of the cell. In the center of the cap is the dense granular base that appears to give rise to the filamentous spike which is the characteristic of the mature sperm. This work is preliminary to an understanding of the mature sperm and future experiments dealing with intra- and inter-species in vitro fertilization.Biology and Biochemistry, Department o