Comparative morphology of the reproductive system of seven species of ostariophysan fishes from the upper Das Velhas River, Brazil

Histological and Transcriptomic Insights into the Ovary Development of Hemibarbus labeo Injected with Spawn-Inducing Hormones

Naturally, the ovaries of many farmed fish can only develop to stage IV (mainly including stage IV oocytes, known as full-grown postvitellogenic oocytes). Therefore, spawn-inducing hormone injections are used to promote ovary development and oocyte maturation, facilitating reproduction in the aquaculture industry. The study of spawn-inducing hormones and their underlying neuroendocrine mechanisms has been a recent focus in fish reproductive biology. However, the intra-ovarian regulatory mechanisms of ovary development and oocyte maturation after hormone injection require further investigation. In this study, we explored the histological and transcriptomic map of the ovary of Hemibarbus labeo after hormone injection to reveal changes in the ovary. The gonad index significantly increased after hormone injection for 5.5 h, after which no significant change was observed. Histological analysis showed that the nuclei had moved to one side of the oocytes at 5.5 h after hormone injection. Moreover, the volume of the oocytes increased and their yolk membranes thickened. Oocytes then underwent their first meiotic division at 5.5-11 h after hormone injection. Subsequently, the follicular membrane was ruptured, and ovulation was completed at 11-16.5 h after hormone injection. In addition, we identified 3189 differentially expressed genes (DEGs) on comparing the transcriptomes at different time points after hormone injection. These DEGs were significantly enriched in the GO terms of nervous system process, molecular transducer activity, and extracellular region, and the KEGG pathways of TNF signaling and cytokine-cytokine receptor interaction; these may play important roles in ovary development and oocyte maturation. Within these pathways, genes such as apoe, creb3, jun, junb, il11, and il8 may play important roles in steroid hormone synthesis and ovulation. Conclusively, our results show detailed sequential dynamics of oocyte development and provide new insights into the intra-ovarian regulatory mechanisms of ovarian development and oocyte maturation in H. labeo. These findings may be important for research on improving egg quality and reproduction in aquaculture.

Comparative reproductive biology of two sympatric Hypostomus in a Neotropical river

Congeneric species often coexist in sympatry using behavioral and morphological adaptations to reduce competition and interspecific interference, but reproductive patterns behind coexistence remain unknown. We analyzed the gonadal morphology and development, reproductive cycle, and population structure of two sympatric congeneric fishes to evaluate the degree of overlap and differentiation of the reproductive biology between species in a Neotropical river. Development of testes and ovaries were similar between species, both showing asynchronous gonadal development, large diameter of gametes and synthesis of mucosubstances by follicle cells to form adhesive eggs. Although the morphometry of germ cells did not present differences, the zona radiata of mature eggs in Hypostomus garmani was markedly thicker than H. francisci, which suggests different spawning habitats. Both species have greater reproductive activity in the rainy season, concomitant with increase in water temperature, however H. garmani initiates and ends its reproduction earlier than H. francisci, indicating a differentiation of reproductive periods. Sexually mature males and females of H. francisci reproduced at a larger mean size then H. garmani. The two congeneric species had a similar abundance and sex ratios in the study area. Results show that although the species exhibited broad overlap of reproductive traits, a spatial and temporal differentiation of the reproductive biology was present. This study contributes to understanding reproductive mechanisms that may facilitate coexistence between congeneric sympatric species.

GMF, Pantoja JCD, Oliveira RS, Mendes YA, Nunes JLG, Ferreira MAP, Rocha RM. Subfamily hypostominae: similarities and differences in testicular structure of amazonian fish

Background

Hypostominae is a subfamily of the family Loricariidae that has a great diversity of species. Accordingly, testicular studies in fish can contribute to the phylogeny and taxonomy of species and to the comparison of reproductive aspects between species. Thus, this work aimed to characterize the testicular morphology and spermatogenesis of the Hypostominae species Baryancistrus xanthellus, Peckoltia oligospila and Hypancistrus zebra.

Results

B. xanthellus, P. oligospila and H. zebra had an anastomosed tubular type of testis. The germinal epithelium was continuous with unrestricted spermatogonia, and the proliferative, meiotic and spermiogenic phases were defined in all species. In the spermiogenic phase, spermatids were classified as initial, intermediate and final. Only in B. xanthellus in the final phase was there nuclear rotation. The sperm for the three species had a head with an oval shape and a single flagellum composed of the short midpiece, principal piece and end piece. B. xanthellus and P. oligospila showed a cylindrical flagellum and H. zebra showed projections that produced a flattened appearance.

Conclusions

On the basis testicular structure and ultrastructural characteristics of the germ cells, there was a greater relationship between B. xanthelus and P. oligospila, while H. zebra had particular characteristics. These aspects show that despite belonging to the same subfamily, the species have distinct biological characteristics.

Integrated use of biomarkers to evaluate the reproductive physiology of Astyanax fasciatus and Hoplias malabaricus males (Teleostei: Characiformes) in polluted reservoirs

The reproductive physiology of fish can be changed by the presence of pollutants in the water, which act as endocrine disrupting compounds (EDC). We evaluated the impacts of water contaminants in polluted reservoirs acting as possible EDC on the reproductive physiology of Astyanax fasciatus and Hoplias malabaricus males. We used biomarkers with different levels of biological organization. Hoplias malabaricus adult males were collected in the summer and winter at five different sites in the Tietê River Basin: the Ponte Nova reservoir (PN), considered a reference site due to the low anthropogenic influence; the Billings reservoir (BIL) at two different branches; and the Guarapiranga reservoir (GUA) at two different branches. Astyanax fasciatus adult males were collected at PN and BIL. BIL and GUA are subjected to great anthropogenic action. We analyzed gonadal histomorphology, testosterone (T), 11-ketotestosterone (11-KT), estradiol (E₂) plasma levels, and gene expression of hepatic vitellogenin (vtgA) and pituitary follicle stimulating hormone (fshβ). In the PN reservoir (reference), the biomarkers analyzed in both species did not differ between the periods analyzed. This is an evidence that the animals keep the same reproductive activity during both seasons. The changes in the plasma concentration of gonadal steroids in both species in polluted reservoirs suggest the presence of EDC compounds in the water and/or adjusts of the physiological setpoint to allow the reproduction in such adverse conditions. The use of vtgA as biomarker suggests the presence of estrogenic compounds, mainly in BIL, but with a more evident response of H. malabaricus. However, even considering physiological changes, both species present testes during the maturation phase that allow the reproduction in an environment with a high degree of pollution.

Ultraestrutura e criopreservação de sêmen de jundiá amazônico (Leiarius marmoratus) em cativeiro

RESUMO Os objetivos do presente estudo foram analisar a ultraestrutura do espermatozoide do jundiá amazônico e avaliar a sua criopreservação com três agentes crioprotetores (metanol 10%, DMSO 10% e etilenoglicol 10%) e duas soluções ativadoras (NaCl 0,29% e NaHCO3 1%). Como diluente, foi utilizada uma solução de glicose a 5%, sendo o sêmen envasado em palhetas de 0,25mL e congelado em vapor de nitrogênio (botijão dry shipper). No sêmen fresco, o espermatozoide apresentou comprimento de 25,46±2,54μm, cabeça esférica (1,51±0,18μm), ausência de acrossoma, peça intermediária com formato cônico (0,93±0,17μm), ligeiramente assimétrica, com presença de vesículas, e flagelo único (21,48±2,45μm). O sêmen descongelado apresentou valores mais altos (P<0,05) para duração, vigor e taxa de motilidade espermática com os crioprotetores metanol 10% e DMSO 10%. A duração da motilidade espermática foi maior (P<0,05) com o ativador NaHCO3 1% (21-96 s). O sêmen de Leiarius marmoratus criopreservado com DMSO e metanol apresentou, respectivamente, 7,32±4,21% e 8,94±6,69% de taxa de motilidade. No entanto, os resultados não foram satisfatórios para estabelecer um protocolo para a espécie.

Testicular structure and development of germ cells of Hypophthalmus marginatus Valenciennes 1840 (Siluriformes: Pimelodidae)

The present study was conducted to assess the testicular structure and germ cell ultrastructure of Hypophthalmus marginatus during spermatogenesis. Semen and sections of the mid-region of the testis were collected, processed, and analyzed using optical and electron microscopy. Macroscopically, the testes of H. marginatus were filiform, and the testicular parenchyma was composed of spermatogenic cells that proliferated, organized within spermatic cysts. During spermiogenesis, spermatids had no nuclear rotation. The proximal centriole was perpendicular to the distal centriole, characteristic of type III spermiogenesis. Spermatozoa were released into the lumen of the seminiferous tubules and had an ovoid head without an acrosome, condensed nucleus, and shallow nuclear fossa. The midpiece was short, with a single long flagellum. The flagellum had the typical axoneme structure, with nine pairs of peripheral and a central pair of microtubules. The thin end piece comprised only peripheral microtubules. Spermatogenesis in H. marginatus features filiform testes, cystic spermatogenesis, and type III spermiogenesis.

Integrative approach detects natural hybridization of sympatric lambaris species and emergence of infertile hybrids

Despite its relevance for ecology, evolution and conservation of species, natural hybridization and hybrids biology are still poorly studied in freshwater fish. Here, we tested the hypothesis that sympatric species Astyanax paranae and A. fasciatus are able to interbreed in the natural environment and presented evidence for the first record of hybridization between these species. We analyzed anatomical traits, gametogenesis, reproductive biology, and genetic variations of the COI and S7 genes of both species and putative hybrids. Intermediate morphometric and meristic features were observed in hybrids when compared to A. paranae and A. fasciatus. Overlap in reproductive season was showed for these species, with greater reproductive activity from August to January, but hybrids did not present any sign of gonadal maturation. Oogonia and perinucleolar follicles as well as spermatogonia and primary spermatocytes were found in hybrids, but previtellogenic and vitellogenic follicles, spermatids, and spermatozoa were absent. Moreover, several alterations in gametogenesis were detected, such as interrupted meiosis in both males and females, vacuolated and degenerated germ cells, increased interstitial tissue, and presence of immune cells. Molecular analyses supported the hypothesis of hybridization between A. paranae and A. fasciatus. Overall, our multidisciplinary approach also provides strong evidence that hybrids are infertile.

Oocyte growth, follicular complex formation and extracellular-matrix remodeling in ovarian maturation of the imperial zebra pleco fish Hypancistrus zebra

This contribution describes the growth of oocytes, addressing the formation of structures that compose the follicular complex, as well as the remodeling of the extracellular matrix, specifically laminin, fibronectin and type IV collagen during gonadal maturation. Thirty-seven females of the Acari zebra fish, Hypancistrus zebra were captured and the ovaries were submitted to histological processing for light and electron microscopy and immunohistochemistry techniques. Oogonia and four stages (I – IV) of oocytes were distinguished, and structures such as the postovulatory follicle and atretic oocytes (initial and advanced atresia) were observed. The follicular complex consists of the mature oocyte, zona radiata (Zr1, Zr2 and Zr3), follicular cells, basement membrane and theca. During oocyte growth, proteins of the extracellular matrix showed different intensities of staining. Based on these observations, a model of oocyte growth is proposed to define specific characteristics of the oocyte and the remodeling of the extracellular matrix in the ovary of H. zebra. This model of oocyte growth can be extended to other species of ornamental fishes. This study contributes data for induced fertilization and eventual conservation of this species.

Progestin is important for testicular development of male turbot (Scophthalmus maximus) during the annual reproductive cycle through functionally distinct progestin receptors

In teleost, sex steroid hormones are critical for reproduction. Progestin is known to promote spermiation. To further understand the functions of progestin via its receptors during the annual reproductive cycle in male turbot (Scophthalmus maximus), we observed testicular development, quantified several sex steroid hormones, detected the expression of progestin receptors, and measured various sperm parameters. Results showed that the turbot testicular structure was of the lobular type. During breeding season, a number of spermatocytes (stage III) developed into spermatids (stage IV), then differentiated into sperm during spermiogenesis (stage V), and finally regressed to spermatocytes (stage VI). Concomitant with testicular development, serum progesterone (P4) and 17α,20β-dihydroxy-4-pregnen-3-one (DHP) exhibited higher levels from stage IV to V than other stages. Furthermore, males with higher motility sperm showed higher levels of P4 and DHP compared with fish with lower motility sperm. These results indicated that P4 and DHP might induce spermatogenesis due to seasonal changes. Concurrently, in testes, the nuclear progesterone receptor (pgr) was expressed throughout the reproductive cycle and its level peaked during spermiogenesis while expression of membrane progestin receptor alpha (mPRα) did not change significantly. However, in sperm, mPRα expression was higher than in testes and had a significant positive correlation with curvilinear velocities (VCL), sperm motility, and motility duration. In conclusion, progestin appears to exert a direct pgr-mediated effect on spermiogenesis and improve sperm motility characteristics depending on the abundance of mPRα protein in sperm during spermiation.