Testicular structure in three viviparous species of teleosts in the genus Jenynsia (Anablepidae).

Histological structure of the testes and development of spermatozoa in Jenynsia species is described using light, scanning and transmission electron microscopy. The testis type is restricted spermatogonial, wherein spermatogonia are restricted to the distal ends of lobules, typical of the Atherinomorpha, and spermatogenesis is continuous throughout the year in wild-caught fish. Within the testicular lobes there are lobular germinal compartments wherein the functional units are spermatocysts, whose borders are formed by Sertoli cells. Spermatocysts may contain meiotic primary spermatocytes, secondary spermatocytes, spermatids, undergoing spermiogenesis, or spermatozoa. Spermatocysts with later stages of developing sperm are located proximal to the testicular ducts. During spermiogenesis, spermatid nuclei become elongated. As this occurs, the nucleus develops a deep, central fossa that contains the centriolar complex. As the flagellum grows, enlarging spermatid mitochondria migrate posteriorly alongside the flagellum but remain separated from it by the cytoplasmatic canal, an indentation of the plasma membrane. Between the enlarged mitochondria and plasma membrane, a sub-mitochondrial net develops. In longitudinal sections, the enlarged mitochondria are stacked in a zig-zag fashion, and in transverse sections they appear as a ring surrounding the flagellum, but separated from it by the cytoplasmic canal. Spermatozoa of the 3 jenynsiid species have an introsperm complex composed of a long mid-piece whose flagellum has a single "wing." Within the efferent ducts and the tubular gonopodium, sperm are lightly packed in a side by side fashion which facilitates their transfer into the female reproductive tract. This study presents detailed descriptions of testicular organization and cytological characterization of the stages of spermatozoa differentiation in 3 species of Jenynsia from northwestern Argentina (J. alternimaculata, J. multidentata and J. maculata), in order to contribute to the understanding of testicular structure and development of spermatozoa in the context of evolution of viviparity in this fish lineage.

Gonadotropin-releasing hormones, including a novel form, in snook Centropomus undecimalis, in comparison with forms in black sea bass Centropristis striata.

The molecular forms of gonadotropin-releasing hormone (GnRH) in brain-pituitary extracts were determined for snook Centropomus undecimalis and black sea bass Centropristis striata. The extracts were analyzed in both isocratic and gradient high performance liquid chromatography (HPLC) programs. Eluted fractions were tested in radioimmunoassays with 4 different antisera made against 3 distinct GnRH peptides. Results show that snook contain 3 forms of GnRH, all of which are present in males and females irrespective of the stage of the reproductive cycle. Larger quantities of these GnRH peptides are present in snook in the nonreproductive phase than in snook in the reproductive phase. One form of snook GnRH is immunologically and chromatographically similar to salmon GnRH, and a second form is similar to chicken GnRH-II. However, the third snook GnRH appears to be distinct from the 7 known forms of the vertebrate hormone. In contrast, sea bass contain only the salmon GnRH-like and chicken GnRH-II-like forms of GnRH and, hence, appear to match the more usual pattern of GnRH peptides in teleosts. We speculate that one of the GnRH genes was duplicated and then altered in a fish ancestral to snook but not sea bass, even though both species of fish are in the recently evolved Perciformes order.

Regulation of sexual succession in the protogynous black sea bass, Centropristis striatus (Osteichthyes: Serranidae)

Serum levels of 17 beta-hydroxy-4-androstene-3,11-dione (11-KT) and testosterone in the protogynous black sea bass, Centropristis striatus fluctuate annually, correlated with the breeding season. Although serum 11-KT levels in both males and females exhibit seasonality, serum estradiol-17 beta concentrations cycle annually only in the females. Throughout the year, serum estradiol levels in males (127 +/- 56 pg/ml, mean +/- SD) were significantly (P less than 0.05) less than levels in breeding (3,930 +/- 1,390 pg/ml), or nonbreeding females (261 +/- 62 pg/ml). In all female sea bass not undergoing sexual succession, histological examination of the ovary revealed only spermatogonia or ongoing spermatogenesis restricted to the posterior male lamellae; a duct system was nonexistent. In female fish undergoing sexual succession, ovarian tissue was always nonvitellogenic and regressing. Breeding females were not observed to undergo gender change. During sexual succession in the postspawning period, male tissue spread into neighboring female lamellae containing oocytes, gradually replacing them and other female tissue. A male duct system developed on the surface. At any time of year, black sea bass undergoing sexual succession had serum estradiol levels (79 +/- 19 pg/ml) which were significantly less (P less than 0.05) than concurrent female serum estradiol levels. A chi-square test demonstrated that serum estradiol levels in these intersex animals were not significantly different from those of males. The possibility is discussed that sexual succession results from inhibition of ovarian tissue response to steroidogenic gonadotropin.

Structural evidence for two different testicular types in teleost fishes.

Testicular structure in Salmoniformes, Perciformes, Cypriniformes, and Atheriniformes has been examined and reinterpreted on the basis of two different tubular types, distinguished from each other by the intratubular distribution of spermatogonia. In the salmoniform, perciform, and cypriniform teleosts studied, spermatogonia are distributed along the entire length of the testicular tubules. However, in the atheriniform teleosts spermatogonia are restricted to the distal end of the tubule. Sperm development in teleosts is cystic, cysts being comprised of Sertoli-cell processes. In both testicular types described, Sertoli cells phagocytize spermatid residual bodies. Together with the germ cells, they comprise the only intratubular cell types within the teleostean testis. Boundary cells are located immediately outside of the tubule basement membrane. They do not form a complete layer over the tubule surface; therefore, interstitial Leydig cells and blood vessels may border directly upon the tubular basement membrane.

Structure and ultrastructure of the testis and sperm formation in goodeid teleosts.

Testis structure in four species of goodeid teleosts is described. Testicular tubules terminate blindly at the testis periphery where spermatogonia are located. In goodeid teleosts, development of sperm takes place synchronously within cysts whose periphery is made up of a single layer of Sertoli cells. Upon completion of spermiogenesis, spermiation ensues wherein sperm are shed, as spermatozeugmata, into the testis efferent duct system. Subsequently, Sertoli cells, which comprised the cyst periphery, transform into efferent duct cells. Sertoli cells phagocytize residual bodies and are involved in the formation of spermatozeugmata. The structure of the goodeid spermatozeugmatum is quite different from that observed in the related poeciliids. It is concluded, in view of this and other considerations, that the goodeids and poeciliids have independently evolved solutions to the problems of internal fertilization and gestation.

Ultrastructural identification of the Sertoli cell in the testis of the northern pike, Esox lucius.

Identification of the intralobular Sertoli cell in the testis of Esox lucius is based upon residual body phagocytosis. Formerly, this lipid-containing cell type was refereed to as the "lobule boundary cell" and erroneously believed to be homologous to the interstitial Leydig cell.

Sperm development in the teleost Oryzias latipes.

In Oryzias latipes the processes of spermatogenesis and spermiogenesis occur within testicular or germinal cysts which are delimited by a single layer of lobule boundary cells. These cells, in addition to comprising the structural component of the cyst wall, ingest residual bodies cast off by developing spermatids. Therefore, they are deemed to be the homologue of mammalian Sertoli cells. The germ cells within a cyst develop synchronously owing to the presence of intercellular bridges connecting adjacent cells. Since bridges also connect spermatogonia, it seems probable that all of the germ cells within a cyst may form a single syncytium and do not exist as individual cells until the completion of spermiogenesis when the residual bodies are cast off. Significant differences between spermiogenesis in O. latipes and in the related poeciliid teleosts are discussed.

Spermiogenesis in the teleost Gambusia affinis with particular reference to the role played by microtubules.

During nuclear elongation in spermatids of Gambusia affinis, a deep fossa is formed at the base of the nucleus in which the centriolar complex and proximal portion of the flagellum reside. To stabilize the positional relationship between the nucleus and centriolar complex, while nuclear morphogenesis is taking place, a series of microtubules develop which emanate from the centriolar complex and extend to the nuclear envelope lining the fossa. Buttressing microtubules also develop within the nuclear fossa which both originate and insert along the nuclear envelope. These appear to stabilize nuclear shape prior to the time when chromatin condensation has proceeded to the stage where it could lend structural stability to nuclear form. Microtubules develop only after specific nuclear morphogenic events have taken place. It is therefore concluded that the spermatid nucleus is capable of "self-assembly" involving microtubules in a supportive role in addition to stabilizing the nuclear-flagellar relationship in G. affinis. The pattern of nuclear fossa-associated microtubules in G. affinis is significantly different from that observed in other poeciliid teleosts indicating a degree of species specificity with regard to both the timing of appearance and total number of microtubules.