Testis-Ova in Spawning Blue Tilapia, Oreochromis aureus

Hermaphroditism characterized by the presence of oocytes in the testes is described in the blue tilapia, Oreochromis aureus, for the first time. Testis-ova were observed in three of 24 spawning males exhibiting otherwise normal male morphology. The testis-ova appeared non-vitellogenic and lacked a follicle cell layer. It is speculated that the testis-ova did not become vitellogenic due to their association with Sertoli cells and the hormonal environment of the male

Testis-Ova in Spawning Blue Tilapia, Oreochromis aureus

Hermaphroditism characterized by the presence of oocytes in the testes is described in the blue tilapia, Oreochromis aureus, for the first time. Testis-ova were observed in three of 24 spawning males exhibiting otherwise normal male morphology. The testis-ova appeared non-vitellogenic and lacked a follicle cell layer. It is speculated that the testis-ova did not become vitellogenic due to their association with Sertoli cells and the hormonal environment of the male

Critical depinning force and vortex lattice order in disordered superconductors

We simulate the ordering of vortices and its effects on the critical current in superconductors with varied vortex-vortex interaction strength and varied pinning strengths for a two-dimensional system. For strong pinning the vortex lattice is always disordered and the critical depinning force only weakly increases with decreasing vortex-vortex interactions. For weak pinning the vortex lattice is defect free until the vortex-vortex interactions have been reduced to a low value, when defects begin to appear with a simultaneous rapid increase in the critical depinning force. In each case the depinning force shows a maximum for non-interacting vortices. The relative height of the peak increases and the peak width decreases for decreasing pinning strength in excellent agreement with experimental trends associated with the peak effect. We show that scaling relations exist between the distance between defects in the vortex lattice and the critical depinning force.Comment: 5 pages, 6 figure

Phase Behavior of Type-II Superconductors with Quenched Point Pinning Disorder: A Phenomenological Proposal

A general phenomenology for phase behaviour in the mixed phase of type-II superconductors with weak point pinning disorder is outlined. We propose that the ``Bragg glass'' phase generically transforms via two separate thermodynamic phase transitions into a disordered liquid on increasing the temperature. The first transition is into a glassy phase, topologically disordered at the largest length scales; current evidence suggests that it lacks the long-ranged phase correlations expected of a ``vortex glass''. This phase has a significant degree of short-ranged translational order, unlike the disordered liquid, but no quasi-long range order, in contrast to the Bragg glass. This glassy phase, which we call a ``multi-domain glass'', is confined to a narrow sliver at intermediate fields, but broadens out both for much larger and much smaller field values. The multi-domain glass may be a ``hexatic glass''; alternatively, its glassy properties may originate in the replica symmetry breaking envisaged in recent theories of the structural glass transition. Estimates for translational correlation lengths in the multi-domain glass indicate that they can be far larger than the interline spacing for weak disorder, suggesting a plausible mechanism by which signals of a two-step transition can be obscured. Calculations of the Bragg glass-multi-domain glass and the multi-domain glass-disordered liquid phase boundaries are presented and compared to experimental data. We argue that these proposals provide a unified picture of the available experimental data on both high-T$_c$ and low-T$_c$ materials, simulations and current theoretical understanding.Comment: 70 pages, 9 postscript figures, modified title and minor changes in published versio

Male Gonadal Differentiation And The Paedomorphic Evolution Of The Testis In Teleostei

Testis differentiation from representatives of the Otophysi (Cyprinus carpio), Percomorpha (Amatitlania nigrofasciata), and Atherinomorpha (Poecilia reticulata) was comparatively described. In the undifferentiated gonad of C. carpio, the primordial germ cells (PGCs) are scattered throughout the gonads while in A. nigrofasciata and P. reticulata the PGCs are restricted to the ventral periphery. In the dorsal region of the developing gonads, with the exception of C. carpio, somatic cell rearrangements result in the differentiation of the sperm duct. Pre-Sertoli cells wrap around single spermatogonia forming cysts that proliferate forming acinar-clusters. In C. carpio and A. nigrofasciata, the cysts in each acinar-cluster move away from each other, creating a central lumen. In C. carpio, the acinar-clusters then fuse to each other forming tubules that become lined by the germinal epithelium. Subsequently, the tubules anastomose dorsally and create the sperm duct. In A. nigrofasciata, the acinar-clusters elongate, forming lobules that individually connect to the sperm duct. These are lined by the germinal epithelium. In P. reticulata, the spermatogonial cysts remain in the acinar-cluster organization. Subsequently, developing ducts connect each cluster to the sperm duct and lobules subsequently develop. In the differentiated testis of C. carpio and A. nigrofasciata, spermatogonia are distributed along the lengths of the anastomosing tubules or lobules, respectively. However, in P. reticulata, the spermatogonia remain restricted to the terminal end of the lobules. Considering testis ontogeny, the spermatogonial acinar-cluster is the adult characteristic of more derived taxa that approximate the early gonad developmental stages of the basal taxa. 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Annual Changes in Germinal Epithelium Determine Male Reproductive Classes of the Cobia

Five reproductive classes of cobia Rachycentron canadum, caught along the Gulf of Mexico and the south-east Atlantic coast of the U.S.A., are described during the annual reproductive cycle. These are based upon changes in the testicular germinal epithelium and the stages of germ cells that are present: early maturation, mid maturation, late maturation, regression and regressed. During early maturation, the germinal epithelium is continuous from the testicular ducts to the periphery of the testis and active spermatogenesis occurs throughout the testis. In mid maturation, the germinal epithelium near the ducts becomes discontinuous, but it remains continuous distally. In late maturation, a discontinuous germinal epithelium extends all along the lobules to the testicular periphery; lobules are swollen with sperm and there is minimal spermatogenesis. The regression class is characterized by a discontinuous epithelium throughout the testis, sperm storage and widely scattered spermatocysts. Spermatogonial proliferation also occurs along the lobule walls and at the periphery of the testis. In regressed testes, spermatogonia exist only in a continuous or discontinuous germinal epithelium, although residual sperm are nearly always present in the lobules and ducts. The presence or absence of sperm is not an accurate indicator of reproductive classes. At the periphery of the testis in the regression and regressed classes, the distal portions of lobules elongate as cords of cells containing spermatogonia and Sertoli cells. All reproductive classes can be identified in paraffin sections, although plastic sections provide better resolution. Using maturation classes defined by changes in the germinal epithelium to describe testicular development and spermatogenesis gives a more accurate picture than does using the traditional terminology. (C) 2002 The Fisheries Society of the British Isles