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We investigated blood gas, hematological and biochemical parameters, and gill morphology of Lophiosilurus alexandri juveniles submitted to hypoxia for 48 h, followed by recovery for 48 h. A total of 48 juveniles (360.0 ± 141.6 g) were distributed among eight tanks (120 L) and subjected to hypoxia condition (water with dissolved oxygen at 2.12 ± 0.90 mg L−1) or normoxia (at 5.60 ± 0.31 mg L−1). Blood gas values (pH, PvCO2, PvO2, sO2, HCO3−, stHCO3−, and base excess) in hypoxia were significantly different from normoxia, while for lactate and the electrolytes (K+, Na+, Cl−, and Ca2+) there was no significant change among treatments. The erythrocytes differed significantly between normoxia and hypoxia at 72 h (24 h of recovery), while for hemoglobin and hematocrit there were no significant differences. There was a significant difference in glucose, triglycerides, and cholesterol for both normoxia and hypoxia, while plasma protein remained unchanged. All gill components (epithelial cells, erythrocytes, pillar cells, mucous cells, ionocytes, undifferentiated cells, and blood capillary lumen) differed significantly between normoxia and hypoxia. A reduction in the length of the primary lamella was observed in the hypoxia and recovery treatments, when compared to normoxia. The secondary branchial lamella showed no significant difference for both treatments. Juveniles of Lophiosilurus alexandri adapted well to hypoxia for 48 h, as they were able to adjust most of their physiological variables to survive this stress condition. After 48 h of hypoxia recovery, fish showed parameters similar to animals in normoxia. Thus, the present study shows that the tolerance to hypoxia conditions of L. alexandri, together with other important beneficial characteristics of the species, such as the high meat quality and high commercial value, demonstrates its great potential for production among regional species.

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.

Although herbicides have been developed to act on the physiological processes of plants, they are responsible for causing deleterious effects on animals. These chemical compounds are widely used throughout the world, but especially in countries that export agricultural products such as Central and South America, their use has increased in recent years. Aquatic environments are natural reservoirs of herbicides, which after being applied on crops, run off through the soil reaching rivers, lakes, and oceans. Fish are among the many organisms affected by the contamination of aquatic environments caused by herbicides. These animals play an important ecological role and are a major source of food for humans. However, few studies address the effects of herbicides on fish in this region. Thus, in the present review we discuss the morphophysiological and molecular consequences of herbicide exposure in Neotropical fish systems as well as how the environmental and land use characteristics in this region can influence the toxicity of these pollutants. A toxicity pathway framework was developed summarizing the mechanisms by which herbicides act and endpoints that need to be further investigated.

SummaryThe present study evaluated the effects of low salinity on the early larval development of Oreochromis niloticus, specifically histological damage to white muscle, morphology of the yolk-sac surface and trunk area, and molecular expression of apoptosis and cell proliferation biomarkers. Newly hatched larvae were submitted to four salinity treatments for a period of 48 or 72 h, in duplicate: (S0) freshwater, (S2) 2 g l−1, (S4) 4 g l−1, and (S6) 6 g l−1NaCl. Larval development was examined using histology, electron microscopy, enzyme-linked immunosorbent assay (ELISA), and morphometry. At the yolk-sac surface, larvae of S4 and S6 displayed alterations to the apical opening of chloride cells that may be related to osmotic expenditure caused by the increased salinity. Caspase-3 expression did not differ significantly among treatments, however significantly lower proliferating cell nuclear antigen (PCNA) expression (P < 0.05) suggested minor cell proliferation in larvae of S4 and S6 compared with S0 and S2. Furthermore, there was a significant reduction in both trunk area and percentage of normal white muscle fibres (WF) in larvae of S4 and S6. Vacuolated areas and myofibrils concentrated at the cell periphery and found in the white muscle from larvae exposed to saline environments suggested disturbance to muscle development. Oedema and mononuclear infiltrate were also observed in the white muscle of S4 and S6 larvae. Together these results indicated that treatments with 4 and 6 g l−1 NaCl may cause osmoregulation expenditure, morphological alterations to the yolk-sac surface and histological damage to skeletal muscle that negatively affected the early larval development of O. niloticus.

Discharge of municipal wastewater promotes the entry of diverse oestrogenic compounds into the water bodies. This complex mixture of substances interferes in the steroidogenic pathway, being able to promote severe reproductive impairment in freshwater fish populations. The purpose of the present study was to evaluate the effects of oestrogenic endocrine disruptors (EDCs) mixture on gonadal sex steroids (testosterone, T; 11-ketotestosterone, 11-KT; 17β-oestradiol, E2; 17-hydroxyprogesterone, 17-OHP) in the peak of the reproductive season of Astyanax rivularis, correlating the results obtained with the proportion of germ cells and gonadal histopathology. Three sampling sites were chosen to conduct the study, one reference site (S1), without contamination by municipal wastewater and two sites (S2 and S3) receiving discharge of municipal wastewater. Males of A. rivularis presented higher concentrations of E2, lower androgens (T and 11-KT) in gonads when compared to males from site S1. Concentrations of 17-OHP did not present significant difference among sites. In sites S2 and S3, the proportion of early spermatocytes, spermatids and Leydig cells increased while spermatozoa decreased compared to fish from S1. The following gonadal histopathologies were detected in the male fishes: intersex gonads (28% in S3) and testicular degeneration with germinal epithelium exhibiting agglutinated germ cells masses and empty cysts (57% in S2 and 71% in S3). In females, concentrations of T, E2 and 17-OHP did not present significant difference among the sites, however higher 11-KT concentrations were detected in females from sites S2 and S3. A lower proportion of perinucleolar follicles and a higher incidence of vitellogenic follicles, besides, aged oocytes and the presence of eosinophilic proteinaceous fluid in the interstitial compartment were also found in females from impacted sites. These results indicate that the urbanization and consequent release of municipal wastewater containing oestrogenic compounds in the headwater creeks are altering the levels of sex hormones and gametogenesis of A. rivularis. Further studies should be performed to determine whether oestrogenic endocrine disrupters are disrupting the reproduction of A. rivularis.

Follicular atresia is a hormonally controlled degenerative process involving apoptosis of the somatic and germ cells. Since different signaling pathways can induce cell death, the aim of the present study was to investigate cell death signaling and crosstalk between autophagic, apoptotic, and lysosomal proteins during follicular atresia in Nile tilapia. For this, females were kept in controlled conditions for 21 days, and ovary samples were collected weekly. The atretic follicles (AF) were analyzed in three regression phases: Early, advanced, and late. Under electron microscopy, the follicular cells exhibited numerous protein synthesis organelles in the early AF. Immunoreactivity for Bcl2, Beclin1, Lc3, and Cathepsin D increased significantly in advanced AF (p < .001), when follicular cells were in intense yolk phagocytosis. In this phase, autophagosomes and autolysosomes were frequently observed. In the late AF, follicular cells had a markedly electron-lucid cytoplasm and immunoreactivity for Bax and TUNEL assay indicated an elevated apoptosis rate. Colocalisation of Lamp1/Cathepsin D and Lc3/Caspase-3 suggests dynamic crosstalk between the autophagy, apoptosis, and lysosome pathways. Taken together, the data indicate that autophagy plays a role in the homeostasis and clearance of the follicular cells preceding Cathepsin D mediated apoptosis during follicular atresia in Nile tilapia.

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.

Hydroelectric power plants (HPP) constitute one of the main forms of energy generation in the world, and its operation produces underwater noise through generators and turbines, which can potentially impact the aquatic fauna. Anthropogenic noise is a stressful factor and can affect behaviour, physiology and acoustic communication of many animal species. However, the noise impact produced by HPP on fishes has not been studied yet. In this research we investigated the noise impact of hydroelectric turbines on the behaviour of Leporinus taeniatus held captive in Brazil. We tested the hypothesis that noise could disturb fishes’ behaviour by affecting school organization, fish position in the tank and the speed of swimming. Two groups of 10 individuals were exposed to 30 sessions of noise played at an intensity of 100 dB re 1 µPa, during 40 s on days 0, 7 and 14. Behavioural data were obtained before, during, and after noise exposure. Results showed that the fish swam significantly faster, moving to the bottom and swimming in depolarised shoals during noise exposure in both groups. Temporal analysis showed that during noise exposure fish swam faster, were less stationary and used the bottom of the tanks more throughout sampling period. These data provide evidence that fish behaviour can be affected by the aversive stimulus of the noise of a hydroelectric turbine in operation. It also suggests that sound pollution issues should be taken into consideration when regulating the use of natural areas for HPP.

We investigated blood gas, hematological and biochemical parameters and gill morphology and morphometry of Lophiosilurus alexandri juveniles submitted to hypoxia for 48 hours followed by recovery for 48 hours. A total of 48 juveniles (360.0 ± 141.6 g) were distributed among eight tanks (120 L) and subjected to hypoxia condition (water with dissolved oxygen at 2.12 ± 0.90 mg L− 1) or normoxia (at 5.60 ± 0.31 mg L− 1). Blood gas values (pH, PvCO2, PvO2, sO2, HCO3−, stHCO3− and base excess) in hypoxia were significantly different from normoxia, while lactate and the electrolytes (K+, Na+, Cl−, Ca2+ and HCO3−) there was no significant change among treatments. The erythrocytes differed significantly between hypoxia and normoxia at 24 h of recovery, while for hemoglobin and hematocrit there were no significant differences. There was a significant difference in glucose, triglycerides, and cholesterol for both normoxia and hypoxia, while plasma protein remained unchanged. All gill components (epithelial cells, erythrocytes, pillar cells, mucus cells, chloride cells, undifferentiated cells, and blood capillary lumen) differed significantly between hypoxia and normoxia. A reduction in the length of the primary lamella was observed in the hypoxia and recovery treatments, when compared to normoxia. The secondary branchial lamella showed no significant difference for both treatments. In general, juveniles of L. alexandri adapted well to hypoxia exposure for 48 h, as they were able to adjust most of their physiological variables to survive this stress condition and return to normoxia within 48 h.

The success of fishes in different environments is related with the variation of reproductive strategies developed by the systematic group, which is reflected in the morphology of the reproductive system and can have ecological and evolutionary implications. This study comparatively analyzed the morphological characteristics of the male and female reproductive systems of ostariophysan fish species from the upper Das Velhas River in the Sao Francisco River basin, Brazil. In order to accomplish this, 393 specimens belonging to seven fish species were sampled between April 2010 and June 2015 for histological, ultrastructural, histochemical, and morphometric analyses. All the species examined have anastomosing tubular testes with unrestricted distribution of spermatogonia. Astyanax bimaculatus, A. fasciatus, A. scabripinnis, and Harttia torrenticola had their spermatozoa embedded in a glycoprotein secretion within the tubule lumen. Most species had type I spermiogenesis, whereas Rhamdia quelen had type III spermiogenesis. While all females examined had asynchronous oocyte development, there were remarkable morphological, histochemical, and morphometric differences in the ovarian follicles and enveloping layers. Hoplias malabaricus and H. torrenticola, which exhibit parental care behaviour, had a significantly larger diameter of vitellogenic oocytes and larger spermatozoa nuclei. Apareiodon ibitiensis, H. torrenticola, and A. scabripinnis, species that have rheophilic preferences, exhibited a thicker zona radiata than the other species examined. The follicular cells of R. quelen and H. torrenticola were columnar and produced a jelly coat and mucosubstances, respectively. The females of the seven fish species studied show a correlation of the reproductive strategies with the reproductive system morphology, while males retained more similar morphological characteristics between species. J. Morphol. 278:170-181, 2017. © 2016 Wiley Periodicals,Inc.

The present study evaluated the effects of low salinity on the early larval development of Oreochromis niloticus, specifically histological damage to white muscle, morphology of the yolk-sac surface and trunk area, and molecular expression of apoptosis and cell proliferation biomarkers. Newly hatched larvae were submitted to four salinity treatments for a period of 48 or 72 h, in duplicate: (S0) freshwater, (S2) 2 g l-1, (S4) 4 g l-1, and (S6) 6 g l-1NaCl. Larval development was examined using histology, electron microscopy, enzyme-linked immunosorbent assay (ELISA), and morphometry. At the yolk-sac surface, larvae of S4 and S6 displayed alterations to the apical opening of chloride cells that may be related to osmotic expenditure caused by the increased salinity. Caspase-3 expression did not differ significantly among treatments, however significantly lower proliferating cell nuclear antigen (PCNA) expression (P0.05) suggested minor cell proliferation in larvae of S4 and S6 compared with S0 and S2. Furthermore, there was a significant reduction in both trunk area and percentage of normal white muscle fibres (WF) in larvae of S4 and S6. Vacuolated areas and myofibrils concentrated at the cell periphery and found in the white muscle from larvae exposed to saline environments suggested disturbance to muscle development. Oedema and mononuclear infiltrate were also observed in the white muscle of S4 and S6 larvae. Together these results indicated that treatments with 4 and 6 g l-1 NaCl may cause osmoregulation expenditure, morphological alterations to the yolk-sac surface and histological damage to skeletal muscle that negatively affected the early larval development of O. niloticus.

Understanding the influence of different temperature conditions on the spermatogenesis is important for improvement of the fish aquaculture. This study evaluated the influence of low temperature on structural and quantitative dynamics of the spermatogenesis in Oreochromis niloticus. Adult males were cultivated with room temperature water (20.28-22.46°C) and testes were collected for histological, ultrastructural and morphometric analyses. This species has unrestricted lobular testis with cystic spermatogenesis and type I spermiogenesis that results in a single anacrosomal aquasperm. Seminiferous lobules and spermatogenic cells had a radial arrangement toward the spermatic duct. Superior and central portions of testes had a greater lobular area than the inferior portion in all samplings. Spermatogonia (9.3%) were distributed in the inferior portion of testes, spermatocytes (25.3%) and spermatids (34.4%) in the central portion, while spermatozoids (39.4%) and secretory cells (4.6%) in the superior portion. Throughout the study, correlation between water temperature and lobular area characteristics was significant only in the inferior portion of testes (r(2)=0.95), although the lobular area in the other testicular portions increased when the water temperature increased by 2°C. Correlation between the water temperature and spermatogenic cells was significant for undifferentiated spermatogonia (r(2)=0.54) and number of spermatids (r(2)=0.67). It is concluded that low cultivation temperatures may positively influence the generation of primary spermatogonia in the inferior periphery of O. niloticus testes. In addition, males maintain reservoirs of germ cells at low temperatures and the radial zonation of spermatogenesis has an important role in the renewal and production of germ cells.

Environmental disasters such as the rupturing of mine tailings dams are a major concern worldwide. In the present study, we assess the effects of the release of mine waste due to the rupture of the Fundão dam on two native fish species (Hoplias intermedius and Hypostomus affinis) from the Doce River basin. Two sampling sites were chosen: S1, a reference site, and S2, contaminated by mining waste. Water and sediment were collected to evaluate metals concentration. Adult fish were caught to analyse biological parameters, hepatic histopathology, and biomarkers of metal contamination. Compared to site S1, the concentration of manganese was statistically higher in water while lead, nickel, and arsenic were statistically higher in the sediment from site S2, and iron had no significant difference between sites. At site S1, fish of both species presented hepatic tissue with normal architecture. At site S2, hepatic alterations, such as cytoplasmic vacuolization and necrosis were frequently found in both species. Regarding the histopathological index, higher values were found in both species from site S2. The positive antibody reactions for cytochrome P450 1A (CYP1A) and metallothionein (MT) were statistically greater in site S2 for both species. The oxidative stress biomarkers, superoxide dismutase (SOD) and catalase (CAT) were statistically higher in H. intermedius from site S2, but only CAT was statistically greater in H. affinis at site S2. These results demonstrate that the release of mineral residues from the rupture of the Samarco mine dam is provoking hepatic damage in the fish from the Doce River besides inducing the expression of proteins and enzymes related to metal contamination.

Food restriction is part of the life cycle of many fish species; however, nutritional deficiency may negatively influence gametogenesis and gonadal maturation. The aim of this study was to evaluate the effects of food restriction on the spermatogenesis of Nile tilapia. For this, adult males were submitted to starvation and refeeding cycles (alternating periods of starvation and feeding) for 7, 14, 21, and 28 days. After 7 days of starvation, glycaemic and lipid levels were significantly reduced, followed by reduction of plasma testosterone (T) and 11-ketotestosterone (11-KT). In addition, reduced proliferation of spermatogonia and increased apoptosis of spermatocytes, spermatids, and spermatozoa was observed in starvation groups. In the refeeding groups, the sex steroids and the proportion of germ cells had no significant alterations compared to the control group, except for spermatozoa. In this sense, the present study suggests that starvation after 7 days progressively reduces T and 11-TK, resulting in damage to the production of spermatogenic cells, while refeeding may delay spermatogenesis but does not lead to testicular impairment.

To support sperm production, fish testes undergo intense tissue remodelling, with endocrine, paracrine and autocrine signals regulating gonad physiology. The aim of this study was to investigate the testicular expression of insulin-like growth factor (Igf) 1 and Igf2 during spermatogenesis, and their relationship with cell proliferation and apoptosis throughout the reproductive cycle. The study was performed in male Hypostomus garmani, a catfish living in headwater rivers of the São Francisco River basin, Brazil. Spermatogenesis was analysed using histology, morphometry, immunohistochemistry and terminal deoxyribonucleotidyl transferase-mediated dUTP–digoxigenin nick end-labelling (TUNEL) analysis at different maturity stages. The results showed the proliferation of spermatogonia throughout the reproductive cycle, with a higher rate during the ripe stage. Germ and Sertoli cells expressed Igf1 at all stages of testicular maturity, Igf2 was predominant at the ripe stage and both Igf1 and Igf2 occurred at the spent stage. Caspase-3 and TUNEL analysis revealed a higher rate of apoptosis at the spent stage associated with reduced expression of Igf1 and Igf2. Sertoli cell proliferation was associated with spermatogonia and spermatocyte cysts at different stages of the reproductive cycle. Together, the data support a proliferative role for Igf1 and Igf2 in regulating testicular apoptosis in H. garmani, with cyclical variation in their expression during gonad maturation.

Oestrogens participate in various biological processes such as oogenesis, vitellogenesis and testicular development, but studies regarding the distribution and protein levels of oestrogen receptors (ERα and ERβ) and aromatase (Cyp19) in testis are rarely investigated in fish species. The aim of the present study was to analyse the expression pattern of ERα, ERβ and Cyp19 in testis of Astyanax rivularis and, in addition, to verify if oestrogenic contamination interferes in the expression levels of these proteins. Quarterly, field samplings were carried out during a reproductive cycle in a stream of the Upper Velhas River with a good conservation status (site S1). In the gonadal maturation peak (June), when ripe stage was most abundant, fish collection was made in three streams: S1, reference site, and S2 and S3, sites contaminated by untreated sewage. The results of immunohistochemistry demonstrated labelling of Cyp19 in Leydig cells and acidophilic granulocytes, but spermatogonia, Sertoli cells, spermatids and spermatozoa were also labelled. ERα was more widely distributed than ERβ being found in all developmental germ cell phases. On the other hand, ERβ was found only in spermatogonia and spermatocytes. During testicular maturation, ELISA levels for Cyp19, ERα and ERβ followed the gonadosomatic index (GSI) with significant higher values in the ripe stage. Regarding to endocrine disruption, the males exposed to domestic sewage presented significant higher expression of Cyp19 and ERα when compared to the non-exposed fish. Together, our results demonstrate expression patterns of Cyp19, ERα and ERβ in the testis of A. rivularis. In addition, we indicate ERα and Cyp19 as sensitive biomarkers for monitoring of oestrogenic contamination in freshwater environments.

The present study assessed the influence of salinity and temperature on body growth and on muscle cellularity of Lophiosilurus alexaxdri vitelinic larvae. Slightly salted environments negatively influenced body growth of freshwater fish larvae and we observed that those conditions notably act as an environmental influencer on muscle growth and on local expression of hypertrophia and hypeplasia markers (IGFs and PCNA). Furthermore, we could see that salinity tolerance for NaCl 4gl(-)(1) diminishes with increasing temperature, evidenced by variation in body and muscle growth, and by irregular morphology of the lateral skeletal muscle of larvae. We saw that an increase of both PCNA and autocrine IGF-II are correlated to an increase in fibre numbers and fibre diameter as the temperature increases and salinity diminishes. On the other hand, autocrine IGF-I follows the opposite way to the other biological parameters assessed, increasing as salinity increases and temperature diminishes, showing that this protein did not participate in muscle cellularity, but participating in molecular/cellular repair. Therefore, slightly salted environments may provide adverse conditions that cause some obstacles to somatic growth of this species, suggesting some osmotic expenditure with a salinity increment.

Sexual differentiation and early gonadal development are critical events in vertebrate reproduction. In this study, the initial testis development and expression of the Vasa, Nanos2 and Sox9 proteins were examined in Nile tilapia Oreochromis niloticus submitted to induced sex reversal. To that end, 150O. niloticus larvae at 5 days post-hatching (dph) were kept in nurseries with no hormonal addition (control group) and 150 larvae were kept with feed containing 17α-methyltestosterone to induce male sex reversal (treated group). Morphological sexual differentiation of Nile tilapia occurred between 21 and 25 dph and sex reversal resulted in 94% males, whereas the control group presented 53% males. During sexual differentiation, gonocytes (Gon) were the predominant germ cells, which decreased and disappeared after that stage in both groups. Undifferentiated spermatogonia (Aund) were identified at 21 dph in the control group and at 23 dph in the treated group. Differentiated spermatogonia (Adiff) were found at 23 dph in both groups. Vasa and Nanos2 occurred in Gon, Aund and Adiff and there were no significant differences between groups. Vasa-labelled Adiff increased at 50 dph in both groups and Nanos2 presented a high proportion of labelled germ cells during sampling. Sertoli cells expressed Sox9 throughout the experiment and its expression was significantly greater during sexual differentiation in the control group. The results indicate that hormonal treatment did not alter initial testis development and expression of Vasa and Nanos2 in Nile tilapia, although lower expression of Sox9 and a delay in sexual differentiation was detected in the treated group.

The Nile tilapia is one of the most important fish species for aquaculture worldwide. Understanding their reproductive biology is essential for improving their aquaculture methods. The morphological and quantitative dynamics of ovarian recrudescence of Oreochromis niloticus was studied for 21 days postspawning. To accomplish this, breeding females were kept in controlled conditions and ovarian samples were collected weekly for histological, ultrastructural and morphometric analyses. Ovarian follicle morphology revealed an intense synthesis activity of the follicular cells, which actively contributed to formation of the zona radiata and oocyte development following spawning. Recently spawned ovaries contained follicles at all developmental stages, but they were predominantly early primary growth (∼ 42%) and full-grown follicles (∼ 20%). Remnants of spawning, postovulatory follicle complexes represented approximately 5% of the former ovarian follicles immediately after spawning, and less than 1% after 7 days. Atretic follicles accounted for approximately 2% of the follicles studied during the period. The stock of primary growth follicles was stable during ovarian recrudescence, indicating their availability for continuous recruitment. Only the frequency of full-grown follicles significantly increased in the ovaries during recrudescence, representing approximately 35% of the follicles 21 days postspawning. The diameters of all follicles were significantly different between the periods analyzed. The ovaries' morphological characteristics, the maintenance of young follicles stocks and the gradual and significant increase in the proportion and diameter of full-grown follicles showed a rapid ovarian recovery and follicular growth of O. niloticus, in 21 days at 29.5°C, necessary for the next spawning.

The Velhas River is the most polluted river in the state of Minas Gerais, south-eastern Brazil. Due to its historical and environmental relevance, the aim of this study was to evaluate the effects of oestrogenic endocrine disruptors on the reproduction of the lambari Astyanax rivularis, a small-sized species found in headwaters of the Sao Francisco River basin. Quarterly field samplings were carried out during a reproductive cycle in three streams of the upper Velhas River: S1 (reference site) and S2 and S3 (sites contaminated by untreated sewage). The main oestrogenic compounds were evaluated in water using HPLC/MS. Molecular, histological and reproductive biomarkers were assessed in liver and gonad. The results showed higher average concentrations of oestradiol (>200ng/l) in S2 and S3, oestrone (>250ng/l) in S2 as well as oestriol (>200ng/l), bisphenol A (>190ng/l), and nonylphenol (>600ng/l) in S3 compared to S1 (

The success of fishes in different environments is related with the variation of reproductive strategies developed by the systematic group, which is reflected in the morphology of the reproductive system and can have ecological and evolutionary implications. This study comparatively analyzed the morphological characteristics of the male and female reproductive systems of ostariophysan fish species from the upper Das Velhas River in the São Francisco River basin, Brazil. In order to accomplish this, 393 specimens belonging to seven fish species were sampled between April 2010 and June 2015 for histological, ultrastructural, histochemical, and morphometric analyses. All the species examined have anastomosing tubular testes with unrestricted distribution of spermatogonia. Astyanax bimaculatus, A. fasciatus, A. scabripinnis, and Harttia torrenticola had their spermatozoa embedded in a glycoprotein secretion within the tubule lumen. Most species had type I spermiogenesis, whereas Rhamdia quelen had type III spermiogenesis. While all females examined had asynchronous oocyte development, there were remarkable morphological, histochemical, and morphometric differences in the ovarian follicles and enveloping layers. Hoplias malabaricus and H. torrenticola, which exhibit parental care behaviour, had a significantly larger diameter of vitellogenic oocytes and larger spermatozoa nuclei. Apareiodon ibitiensis, H. torrenticola, and A. scabripinnis, species that have rheophilic preferences, exhibited a thicker zona radiata than the other species examined. The follicular cells of R. quelen and H. torrenticola were columnar and produced a jelly coat and mucosubstances, respectively. The females of the seven fish species studied show a correlation of the reproductive strategies with the reproductive system morphology, while males retained more similar morphological characteristics between species. J. Morphol. 278:170-181, 2017. © 2016 Wiley Periodicals,Inc.

We studied the relationship between the morphology of the reproductive system and the reproductive strategies of six neotropical catfishes using macroscopic and microscopic analyses. The reproductive system of the examined Siluriformes showed diversified characteristics, but permitted their being grouped according to three reproductive strategies: pelagic spawning, demersal spawning, and internally fertilizing. The pelagic spawners Pseudoplatystoma corruscans and Conorhynchos conirostris have testes that are characterized by filiform lobes, absence of testicular secretion, full-grown oocytes of small diameter, thin zona radiata, and cuboidal follicular cells. Pimelodus maculatus is morphologically distinct from the other two pelagic spawners catfishes due to the presence of testicular secretion. The demersal spawners Lophiosilurus alexandri and Rhinelepis aspera possess homogeneous testicular secretion, large mature oocytes, and columnar follicular cells. The most specialized reproductive system was observed in the internally fertilizing Trachelyopterus galeatus, which possesses a seminal vesicle accessory to the testes, spermatozoa with elongated nuclei that form spermatozeugmata, and a secretory ovarian lamellar epithelium that is associated with sperm storage. The reproductive system observed in Neotropical catfishes showed a relationship associated with the type of fertilization and the reproductive strategies of the six species studied.

The balance between cell proliferation and apoptosis is crucial for tissue development and homeostasis. The present study investigated the contribution of proliferating cell nuclear antigen (PCNA) and apoptosis during ovarian remodeling after spawning in the Nile tilapia Oreochromis niloticus. Breeding females were kept in controlled conditions and ovary samples were collected weekly for TUNEL assay, immunohistochemistry for PCNA and caspase-3 and morphometric analysis. During the follicular growth, PCNA labeled mainly the nuclei of oocytes and follicular cells in a high proportion of follicles especially in primary growth, while a low occurrence of apoptosis in follicular and theca cells was detected. At 0-3 days post-spawning, post-ovulatory follicles showed no proliferative activity, however the follicular cells exhibited high rates of apoptosis. At 7-10 days, PCNA labeled the thecal cells in a low proportion of post-ovulatory follicles, which showed follicular cells with lower rates of apoptosis. PCNA labeled mainly the theca in the advanced and late stages of atretic follicles, while the follicular cells exhibited a significant increase of apoptosis along follicular atresia. We concluded that PCNA and apoptosis work cooperatively to ensuring the success of follicle development and maintaining of tissue homeostasis during follicular growth. PCNA and apoptosis are also essential mechanisms in the follicular regression during post-spawning ovarian recovery in the Nile tilapia.

The Nile tilapia is one of the most important fish species for aquaculture worldwide. Understanding their reproductive biology is essential for improving their aquaculture methods. The morphological and quantitative dynamics of ovarian recrudescence of Oreochromis niloticus was studied for 21 days postspawning. To accomplish this, breeding females were kept in controlled conditions and ovarian samples were collected weekly for histological, ultrastructural and morphometric analyses. Ovarian follicle morphology revealed an intense synthesis activity of the follicular cells, which actively contributed to formation of the zona radiata and oocyte development following spawning. Recently spawned ovaries contained follicles at all developmental stages, but they were predominantly early primary growth (∼ 42%) and full-grown follicles (∼ 20%). Remnants of spawning, postovulatory follicle complexes represented approximately 5% of the former ovarian follicles immediately after spawning, and less than 1% after 7 days. Atretic follicles accounted for approximately 2% of the follicles studied during the period. The stock of primary growth follicles was stable during ovarian recrudescence, indicating their availability for continuous recruitment. Only the frequency of full-grown follicles significantly increased in the ovaries during recrudescence, representing approximately 35% of the follicles 21 days postspawning. The diameters of all follicles were significantly different between the periods analyzed. The ovaries' morphological characteristics, the maintenance of young follicles stocks and the gradual and significant increase in the proportion and diameter of full-grown follicles showed a rapid ovarian recovery and follicular growth of O. niloticus, in 21 days at 29.5°C, necessary for the next spawning.

CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior O objetivo deste estudo foi avaliar as respostas hemogasométricas, hematológicas e bioquímicas de juvenis de L. alexandri submetidos à hipóxia e posterior recuperação à hipóxia. 48 juvenis de pacamã (360 ± 141,6 g e 26,6 ± 3,0 cm) foram distribuídos e aclimatados durante 15 dias em oito tanques de 120 L em sistema de recirculação de água (temperatura 28,9 ± 0,28 °C, oxigênio dissolvido (OD) 5,10 ± 0,56 mg L-1 e amônia total 0,05 ± 0,01 mg L-1). Os peixes foram alimentados à vontade, duas vezes ao dia, com dieta comercial. O grupo controle corresponde aos peixes submetidos à oxigenação contínua durante 96 h (OD – 5,6 ± 0,31 mg L-1) e o grupo em hipóxia aos peixes submetidos à hipóxia (2,12 ± 0,90 mg L-1) durante 48 h e posterior recuperação às condições de oxigenação (5,30 ± 0,47 mg L-1) por mais 48 h, totalizando 96 h. As coletas foram realizadas nos tempos 24 e 48 h de hipóxia e 24 e 48 h de recuperação. Todos os dados foram submetidos à análise estatística ANOVA de duas vias seguido pelo teste de Tukey (P0,05). Entretanto, houve aumento do stHCO3- às 24 h de hipóxia, em relação ao controle (P0,05). A menor contagem de eritrócitos foi registrada às 48 h de hipóxia (P0,05). Para as variáveis bioquímicas, houve diminuição dos níveis de glicose às 48 h de hipóxia e às 24 h de recuperação, em comparação ao grupo controle (P0,05). Os resultados apresentados dos parâmetros hemogasométricos, hematológicos e bioquímicos neste estudo mostram que os juvenis de Lophiosilurus alexandri se adaptam bem às baixas concentrações de oxigênio dissolvido na água durante 48 h, sem apresentar mortalidade, ajustando suas variáveis fisiológicas para sobreviver nessa condição de estresse e retornando às condições normais após 48 horas de recuperação à hipóxia. The aim of this study was to evaluate the blood gasometric, hematological and biochemical responses of juveniles of L. alexandri submitted to hypoxia and subsequent recovery from hypoxia. 48 pacamã juveniles (360 ± 141.6 g and 26.6 ± 3.0 cm) were distributed and acclimated for 15 days in eight 120 L tanks in a water recirculation system (temperature 28.9 ± 0.28 °C, dissolved oxygen (OD) 5.10 ± 0.56 mg L-1 and total ammonia 0.05 ± 0.01 mg L-1). The fish were fed ad libitum, twice a day, with a commercial diet. The control group corresponds to fish subjected to continuous oxygenation for 96 h (OD - 5.6 ± 0.31 mg L-1) and the group in hypoxia to fish subjected to hypoxia (2.12 ± 0.90 mg L-1) for 48 h and later recovery to oxygenation conditions (5.30 ± 0.47 mg L-1) for another 48 h, totaling 96 h. Collections were performed at times of 24 and 48 h of hypoxia and 24 and 48 h of recovery. All data were subjected to two-way ANOVA statistical analysis followed by the Tukey’s test (P0.05). However, there was an increase in stHCO3- at 24 h of hypoxia, compared to the control (P0.05). The lowest erythrocyte count was recorded at 48 h of hypoxia (P0.05). For biochemical variables, there was a decrease in glucose levels at 48 h of hypoxia and at 24 h of recovery, compared to the control group (P0.05). The results presented for blood gasometric, hematological and biochemical parameters in this study show that juveniles of Lophiosilurus alexandri adapt well to low concentrations of oxygen dissolved in water for 48 h, without present mortality, adjusting their physiological variables to survive in this stress condition and returning normal conditions after 48 h of recovery from hypoxia.

CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior Este trabalho teve por objetivo avaliar o crescimento, tamanho e idade de primeira maturação, níveis hormonais e parâmetros bioquímicos de Lophiosilurus alexandri. Foram utilizados 400 juvenis produzidos no Laboratório de Aquacultura da UFMG. Após completar 90 dias pós-eclosão (DPE) foi iniciada a etapa de crescimento, onde os animais foram acompanhados até os 968 DPE. Durante o experimento, foram realizadas sucessivas amostragens de machos e fêmeas para análise histológica das gônadas, acompanhar o crescimento, mensuração dos índices hepatossomático (IHS) e gonadossomático (IGS). A partir da diferenciação macroscópica das gônadas, foram realizadas coleta de sangue, aos 372, 481, 845 e 968 DPE para análises bioquímicas. Análises hormonais (estradiol, testosterona e 17-hidroxiprogesterona) foram realizadas aos 845 e 968 DPE, quando já foram detectadas gônadas macroscopicamente desenvolvidas. Os dados obtidos foram sempre comparados entre machos e fêmeas de mesma idade e para indivíduos do mesmo sexo em idades diferentes. Não houve diferença para o crescimento em peso e comprimento entre machos e fêmeas (P>0,05). Machos completamente maduros foram encontrados aos 593 DPE, com 29,88±1,76 cm e 444,1±77,03 g. As fêmeas atingiram maturação avançada aos 845 DPE, com 36,51±1,06 cm e 783,05±48,57 g. Todos os hormônios avaliados apresentaram-se em níveis semelhantes entre machos e fêmeas aos 845 DPE (P>0,05). Contudo, aos 968 DPE houve aumento do nível de E2 nas fêmeas, diferindo também do valor encontrado para os machos neste momento (P 0,05). Os resultados do presente trabalho fornecem informações básicas e essenciais para o futuro do manejo da pesca e para o planejamento produção comercial de L. alexandri. This work aimed to evaluate the growth, size and age of first maturation, hormonal levels and biochemical parameters of Lophiosilurus alexandri. Four hundred juveniles produced at the UFMG Aquaculture Laboratory were used. After completing 90 days after hatching (DAH), the growth stage began, where the animals were followed up to 968 DAH. During the experiment, successive sampling of males and females were performed for histological analysis of the gonads, monitoring growth, measurement of hepatosomatic (IHS) and gonadosomatic (IGS) indices. From the macroscopic differentiation of the gonads, blood was collected at 372, 481, 845 and 968 DAH for biochemical analysis. Hormonal analyzes (Estradiol, Testosterone and 17α-hydroxyprogesterone) were performed at 845 and 968 DAH, when macroscopically developed gonads were detected. The data obtained were always compared between males and females of the same age and for individuals of the same sex at different ages. There was no difference for growth in weight and length between males and females (P> 0.05). Completely mature males were found at 593 DAH, with 29.88 ± 1.76 cm and 444.1 ± 77.03 g. The females reached advanced maturity at 845 DAH, with 36.51 ± 1.06 cm and 783.05 ± 48.57 g. All hormones evaluated were at similar levels between males and females at 845 DAH (P> 0.05). However, at 968 DAH there was an increase in the level of E2 in females, also differing from the value found for males at this time (P 0.05). The results of the present work provide basic and essential information for the future of fisheries management and for the commercial production planning of L. alexandri.

CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior Poucas espécies de peixes nativos com potencial para a piscicultura possuem tecnologia de produção totalmente desenvolvida e consolidada para as diferentes fases do cultivo. O objetivo desse estudo foi analisar a gametogênese e maturação gonadal do pacamã, Lophiosilurus alexandri em condições de cultivo, relacionando os parâmetros reprodutivos com as condições fisiológicas dos peixes. Para isso, exemplares adultos (primeira geração filial de reprodutores selvagens) previamente acondicionados em tanque com 10.000 L de água a 23°C no Laboratório de Aquacultura da UFMG (LAQUA) foram transferidos para tanque circular com 3.000 L de água aquecida artificialmente à 27°C. A amostragem dos peixes foi realizada em quatro períodos: a primeira, antes do aquecimento da água (grupo T1, água a 23ºC) e as três subsequentes com 20 e 40 (grupo T2) e 70 dias (grupo T3) após aquecimento da água a 27ºC. Dois casais de L. alexandri foram colocados em tanque de fundo de areia com água aquecida à 27ºC para verificar a formação de ninhos e ocorrência de desova. Os parâmetros físico-químicos da água foram monitorados diariamente para garantir as condições ideais de cultivo. De cada exemplar foram obtidos os dados biométricos, os indicadores fisiológicos e parâmetros sanguíneos dos peixes. Amostras de gônadas e fígado foram coletadas para processamento histológico e imunoensaio de ELISA. A frequência de fêmeas em maturação foi maior no T3, onde foram encontrados os melhores parâmetros reprodutivos: maior IGS, diâmetro dos folículos vitelogênicos e altura das células foliculares, que foram relacionados a elevadas concentrações séricas de 17β-estradiol e níveis hepáticos de vitelogenina. Em contrapartida, no T1 houve alta frequência de fêmeas com ovários em regressão e alto índice de atresia folicular. A fecundidade absoluta no T3 variou de 5.449,364 a 12.581,74 ovócitos por fêmea. Os níveis séricos de 17α-hidroxiprogesterona variaram discretamente entre os tempos de coleta, elevando-se do T2 para o T3, onde as fêmeas alcançaram a maturação final ovocitária. No entanto, não foram encontradas desovas no fundo dos tanques, sequer nos casais mantidos em tanque com fundo de areia. Os níveis séricos de 11-ketotestosterona em machos aumentaram consideravelmente após o aquecimento da água (T2 e T3), porém os parâmetros reprodutivos foram semelhantes nos três grupos de amostragem. A presença de machos intersexo (11%) e, níveis hepáticos de vitelogenina e proteínas da zona radiata semelhante aos das fêmeas, sem uma aparente desorganização da estrutura testicular e da função espermatogênica, alertam para a ocorrência de desregulação endócrina nas condições do cultivo. Diferenças significativas em relação às variáveis hematológicas e bioquímicas foram observadas com o aumento da temperatura (T2 e T3), havendo aumento da glicose sanguínea e número de eritrócitos tanto em fêmeas quanto em machos. Apesar das concentrações séricas de cortisol não diferirem entre os tempos de coleta em machos, em fêmeas houve diferenças significativas entre os tempos T2 e T3. Em conjunto, os resultados indicam que o aumento da temperatura da água estimula a gametogênese e maturação gonadal de L. alexandri em condições de cultivo, sendo as fêmeas mais sensíveis do que os machos às mudanças de temperatura. Manutenção dos peixes em baixas temperaturas da água (23ºC) induz atresia folicular em ovários, que pode reduzir o potencial reprodutivo da espécie em cativeiro. Os parâmetros sanguíneos analisados apresentaram variações fisiológicas e podem ser utilizados como indicadores de saúde de L. alexandri mantidos em cativeiro Few native fish species with potential for fish farming have fully developed and consolidated production technology for the different stages of cultivation. The aim of this study was to analyze the gametogenesis and gonadal maturation of the pacamã, Lophiosilurus alexandri under culture conditions, relating the reproductive parameters with the physiological conditions of the fish. For this, adult specimens (first filial generation of wild breeding) previously kept in a tank with 10,000 L of water at 23°C in the Aquaculture Laboratory of the UFMG (LAQUA) were transferred to circular tank with 3,000 L of artificially heated water at 27°C. Fish sampling was performed in four periods: the first, before water heating (T1 group, water at 23ºC) and the subsequent three periods at 20 and 40 (T2 group) and 70 (T3 group) days after heating water at 27°C. Two couples were placed in a sand-bottom tank with water heated at 27ºC in order to verify the nest formation and spawning occurrence. The physico-chemical parameters of the water were monitored daily to ensure optimum conditions of cultivation. Biometric data, physiological indicators and blood parameters of the fish were obtained from each specimen. Samples of gonads and liver were collected for histological processing and ELISA. The frequency of maturing females was higher in T3, where the best reproductive parameters were found: higher IGS, vitellogenic follicle diameter and follicular cell height, which were associated with the higher serum concentrations of 17β-estradiol and hepatic levels of vitellogenin. On the other hand, there was a high frequency of females with regressing ovaries in T1 and a high index of follicular atresia in ovaries. The absolute fecundity in T3 varied from 5,449.364 to 12,581.74 oocytes per female. Serum levels of 17α-hydroxyprogesterone varied discretely between collection times, rising from T2 to T3, where females reached final oocyte maturation. However, no spawning was found in the bottom of the tank, even when couples were placed in sand-bottom tank. In males, serum levels of 11- ketotestosterone increased considerably after water heating (T2 and T3), but reproductive parameters were similar in all three sampling groups. The presence of intersex males (11%) and levels of vitelogenin and proteins of the zona radiata similar to that of the females, without an apparent disorganization of the testicular structure and spermatogenesis, is a concern regarding the occurrence of endocrine dysregulation in captive conditions. Significant differences in the hematological and biochemical variables were observed in T2 and T3, with increased blood glucose and number of iv erythrocytes in both male and female fish. Although seric concentrations of cortisol did not differ amongst collection times in males, significant differences were observed in females between times T2 and T3. Together, the results indicate that the increase in water temperature stimulates the gametogenesis and gonadal maturation of L. alexandri under culture conditions, with females being more sensitive than males to changes of the temperature. Maintenance of fish at low water temperatures (23ºC) induces follicular atresia in ovaries, which may reduce the reproductive potential of the species in captivity. The blood parameters presented physiological variations, which can be used as health indicators for L. alexandri kept in captivity.

Peixes do gênero Astyanax estão amplamente distribuídos pelas bacias hidrográficas brasileiras, mas permanecem carentes de estudos. Espécies simpátricas, que coabitam o mesmo ambiente, podem eventualmente intercruzar e gerar híbridos. A hibridação apresenta importância para ecologia, conservação e evolução das espécies, portanto sua detecção em ambiente natural é relevante. O objetivo desse trabalho foi analisar comparativamente a gametogênese e a biologia reprodutiva de A. paranae e A. fasciatus da cabeceira do Rio Grande e, verificar por análises moleculares a ocorrência de hibridação natural entre essas espécies, uma vez que um morfótipo intermediário foi amostrado e identificado como Astyanax sp. Um total de 491 exemplares (239 A. paranae, 213 A. fasciatus e 44 Astyanax sp.) foram coletados trimestralmente na cabeceira do Rio Grande entre maio de 2014 e abril de 2015. Os peixes foram eutanasiados, dissecados e tiveram dados biométricos e índices biológicos obtidos. Amostras das gônadas foram coletadas para emprego de técnicas morfológicas (microscopia de luz e eletrônica). Fragmentos das nadadeiras caudais foram coletados e fixados em álcool absoluto para extração e amplificação do DNA utilizando primers para o gene mitocondrial COI e então os produtos de PCR foram sequenciados bidireccionalmente (DNA barcoding). Para todos os peixes coletados, foram determinados estádios de maturação gonadal baseados nas características macro e microscópicas das gônadas e nos valores de IGS. A espécie A. paranae apresentou dimorfismo sexual, com fêmeas significativamente maiores (9,68 ± 0,92 cm) e mais pesadas (12,93 ± 3,89 g) que machos (8,96 ± 0,66 cm; 9,50 ± 2,06 g). Exemplares de Astyanax sp. apresentaram comprimento e peso significativamente maiores (10,85 ± 1,29 cm; 17,37 ± 7,01 g) que A. paranae e uma tendência de maior peso em relação a A. fasciatus (fêmeas: 15,95 ± 5,07 g; machos: 12,86 ± 5,96 g). As maiores médias de IGS foram encontradas nos trimestres agosto-outubro e novembro-janeiro, quando uma maior frequência de peixes maduros foi observada. Astyanax sp. não apresentou maturação gonadal e a média de IGS foi a menor entre os animais amostrados (0,08 ± 0,18). A fecundidade absoluta foi estatisticamente similar em A. paranae (5582,82 ± 1892,78 ovócitos) e A. fasciatus (5668,57 ± 1816,68 ovócitos), mas a fecundidade relativa ao peso gonadal foi maior em A. fasciatus. Análises histológicas, morfométricas e ultraestruturais mostraram características similares das células germinativas de fêmeas e machos das duas espécies. As gônadas de Astyanax sp. apresentaram várias alterações como aumento de tecido intersticial, células germinativas vacuolizadas e em degeneração, organelas alteradas, evidências de apoptose e interrupção da meiose. O DNA barcoding confirmou a identificação morfológica de A. paranae e A. fasciatus e mostrou a existência de haplótipos dessas duas espécies em amostras de Astyanax sp. O compartilhamento de haplótipos mitocondriais de duas espécies distintas por um único morfótipo, as alterações gonadais observadas nesses animais, bem como as evidências de biologia reprodutiva de A. paranae e A. fasciatus sugerem fortemente que o morfótipo intermediário Astyanax sp. é um híbrido natural infértil resultante do cruzamento entre essas duas espécies de lambaris na cabaceira do Rio Grande. Fishes of the genus Astyanax are widely distributed in Brazilian watersheds, but they remain poorly studied. Sympatric species, which cohabit the same environment, may eventually interbreed and generate hybrids. Hybridization is important for the ecology, conservation and evolution of species, so its detection in natural environment is relevant. The aim of this work was to compare the gametogenesis and reproductive biology of A. paranae and A. fasciatus in the headwaters of Grande River and to verify by molecular analysis the occurrence of natural hybridization between these species, since an intermediate morphotype was sampled and identified as Astyanax sp. A total of 491 specimens (239 A. paranae, 213 A. fasciatus and 44 Astyanax sp.) was collected quarterly in the headwaters of Grande River between May 2014 and April 2015. The fish were sacrificed, dissected and had their biometric data and biological index obtained. Samples of gonads were collected for morphological techniques (light and electron microscopy). Caudal fins were collected and fixed in absolute ethanol for DNA extraction and amplification using primers for mitochondrial COI gene and then the PCR products were bidirectionally sequenced. For all fish collected, gonadal maturation stages were determined based on the macro and microscopic characteristics of the gonads and on the GSI values. The species A. paranae presented sexual dimorphism, with females significantly larger (9.68 ± 0.92 cm) and heavier (12.93 ± 3.89 g) than males (8.96 ± 0.66 cm, 9.50 ± 2.06 g). Specimens of Astyanax sp. presented significantly greater length and weight (10.85 ± 1.29 cm, 17.37 ± 7.01 g) than A. paranae and a trend of greater weight when compared to A. fasciatus (females: 15.95 ± 5.07 G: males: 12.86 ± 5.96 g). The highest averages of GSI were found in the August-October and November-January quarters, when a higher frequency of mature fish was observed. Astyanax sp. did not present gonadal maturation and the mean GSI was the lowest among the sampled animals (0.08 ± 0.18). The batch fecundity was statistically similar in A. paranae (5582.82 ± 1892.78 oocytes) and A. fasciatus (5668.57 ± 1816.68 oocytes), but the relative fecundity (body weight) was higher in A. fasciatus. Histological, morphometric and ultrastructural analyses showed similar characteristics of germ cells of females and males of both species. Gonads of Astyanax sp. presented several alterations such as increased interstitial tissue, vacuolated and degenerating germ cells, altered organelles, evidence of apoptosis and interrupted meiosis. The DNA Barcoding confirmed the morphological identification of A. paranae and A. fasciatus and showed the existence of haplotypes of these two species in samples of Astyanax sp. The sharing of haplotypes from two distinct species by a single morphotype, the gonadal alterations observed in these animals, as well as the evidences of reproductive biology of A. paranae and A. fasciatus strongly suggest that the intermediate morphotype Astyanax sp. is a natural infertile hybrid resulting from the crossing between these two species of lambaris in the headwaters of Grande River.