Histopathology and changes in the expression of metallothioneins, heat shock proteins and inducible nitric oxide synthase in Prochilodus costatus from a neotropical river contaminated by heavy metals.

The most recent dam rupture in Brazil released tons of mining tailings into the upper course of the Paraopeba River, affecting this river in an unprecedented way. The present study aimed to evaluate the influence of heavy metals on Prochilodus costatus, an important commercial species in Brazil, four years after the dam colapse. To this end, biomarkers of heavy metals, oxidative stress, and environmental stress were analyzed, and histological analyses of target organs were performed. The results demonstrated critical contamination of fish from the Paraopeba River. Increased expression of Metallothioneins - MTs, Heat Shock Protein - HSP70, and inducible nitric oxide synthase - iNOS, as well as greater rates of histological changes in the liver, spleen, and gonads, were observed in P. costatus. These findings demonstrate that, despite past contamination, the metals present in mining tailings have significantly increased the contamination of the Paraopeba River basin.

Starvation-induced autophagy modulates spermatogenesis and sperm quality in Nile tilapia.

Spermatogenesis is a finely regulated process that involves the interaction of several cellular mechanisms to ensure the proper development and maturation of germ cells. This study assessed autophagy contribution and its relation to apoptosis in fish spermatogenesis during starvation. To that end, Nile tilapia males were subjected to 0 (control), 7, 14, 21, and 28 days of starvation to induce autophagy. Testes samples were obtained for analyses of spermatogenesis by histology, electron microscopy, immunohistochemistry, and western blotting. Sperm quality was assessed using a computer-assisted sperm analysis (CASA) system. Data indicated a significant reduction in gonadosomatic index, seminiferous tubule area, and spermatozoa proportion in fish subject to starvation compared to the control group. Immunoblotting revealed a reduction of Bcl2 and Beclin 1 associated with increased Bax and Caspase-3, mainly after 21 and 28 days of starvation. LC3 and P62 indicated reduced autophagic flux in these starvation times. Immunolabeling for autophagic and apoptotic proteins occurred in all development stages of the germ cells, but protein expression varied throughout starvation. Beclin 1 and Cathepsin D decreased while Bax and Caspase-3 increased in spermatocytes, spermatids, and spermatozoa after 21 and 28 days. Autophagic and lysosomal proteins colocalization indicated the fusion of autophagosomes with lysosomes and lysosomal degradation in spermatogenic cells. The CASA system indicated reduced sperm motility and velocity in animals subjected to 21 and 28 days of starvation. Altogether, the data support autophagy acting at different spermatogenesis stages in Nile tilapia, with decreased autophagy and increased apoptosis after 21 and 28 days of starvation, which results in a decrease in the spermatozoa number and sperm quality.

Reproductive toxicity induced by lead exposure: Effects on gametogenesis and sex steroid signaling in teleost fish.

Lead (Pb) is an emerging contaminant widely distributed in aquatic environments, which has serious effects on human and animal health. In this study, we determined whether Pb exposure affects gametogenesis, sex steroids, estrogen (ERα and ERß), and androgen (AR) receptors. Adult specimens of Astyanax bimaculatus were exposed in duplicate to 15, 50, and 100 µg/L of lead acetate, whereas the control group was not exposed. After 28 days of exposure, fish were euthanized and samples of the gonads, liver, and blood were collected for analysis. The results indicated a reduction in the gonadosomatic index as well as the diameters of the vitellogenic follicles and seminiferous tubules in the exposed groups. Morphometry of gametogenesis revealed inhibition of the secondary oocyte growth and a reduction in the number of spermatozoa in the 50 and 100 µg/L Pb-treated groups. In females, plasma 17ß-estradiol (E2) increased following 15 and 50 µg/L Pb treatment, whereas males exhibited an increase in E2 and 11-ketotestosterone following treatment with 15 and 100 µg/L Pb, respectively. Vitellogenin was significantly reduced in females exposed to 100 µg/L Pb, but metallothionein levels were unchanged. ERα, ERß, and AR were immunolocalized in the somatic and germ cells, with increased ovarian expression of ERα and Erß in the 100 µg/L Pb-treated group, but no significant difference in AR among the groups. In males, only ERα increased in the 100 µg/L Pb-treated group. These results indicate that Pb exposure impairs gametogenesis, disrupts estrogen receptor signaling, and affects the expression of major reproductive biomarkers in A. bimaculatus.

Reproductive and morphological analysis of the trairão Hoplias intermedius in the São Francisco River, downstream from a large reservoir.

Hoplias intermedius, of the Characiformes order and Erytrinidae family, is widely distributed across South America. This commercially interesting species can reach a length of 100 cm and a weight of 15-20 kg. To evaluate the reproductive biology of H. intermedius in the São Francisco River, Brazil, 154 males and 190 females were captured bi-monthly between September 2018 and August 2019 from the downstream regions of the Três Marias dam. Gillnets with differently sized meshes were deployed at distances of 34-54 km after the confluence with the Abaeté River (18°00'49″ S, 45°10'51″ W). Biometric data, gonadosomatic index (GSI), Fulton condition factor (K) and absolute fecundity (AF) were determined for each specimen. Gonad maturation stages and the spawning season were also established. The biometric data, GSI and K average values were relatively higher in females than in males. The reproductive peak for both sexes was reached around January/February. The mean AF was 4300.5 ± 1451.2 follicles per female. Fully developed vitellogenic follicles had a mean diameter of 1014.8 ± 250.7 µm, which is characteristic of fish with moderate fecundity. Fish of all maturation stages, from mature, spawned and spermed, occurred in all bimesters, indicating that this species reproduced throughout the year. The high frequency of spawning females throughout the year and the histological characteristics of spawned ovaries indicated that trairão H. intermedius' spawning type is partial.

Chronic estrone exposure affects spermatogenesis and sperm quality in zebrafish (Danio rerio).

Estrone (E1) is a common environmental contaminant found in rivers and streams due to the farming of animals, such as swine and cattle. Our study evaluated the effects of chronic E1 exposure at environmentally relevant concentrations on spermatogenesis and the semen quality of zebrafish (Danio rerio). We exposed the fish to E1 at concentrations of 20, 200, and 2000 ng/L diluted in 0.001% ethanol (v/v) for 49 days. There were two control groups: one was exposed to water only and the other to ethanol at the same concentration used in the E1 groups. Following exposure, we analyzed the proportion of testicular cell types and other components (%), rate of cell proliferation and death, and sex steroid concentrations. Furthermore, we analyzed the expression of insulin-like growth factor 1 (IGF1), IGF2, IGF1 receptor (IGF1R), and inducible nitric oxide synthase and assessed the semen quality. E1 exposure increased spermatogonia, spermatids, Sertoli cells, Leydig cells, and the proportion of inflammatory infiltrate but decreased the spermatozoa amount. These changes were reflected by reductions in the gonadosomatic index and levels of 11-ketotestosterone in the testes. On the other hand, E1 exposure increased testicular estradiol, IGF1R expression, and nitric oxide production. After an evaluation using a computer-assisted sperm analysis (CASA) system, we observed reduced progressive motility, curvilinear velocity, and beat cross frequency of 20 and 2000 ng/L E1 groups. Our findings support that E1 causes deleterious effects on the testicular function and semen quality of D. rerio even at environmental concentrations. Thus, E1 concentrations should be monitored in surface waters for the purposes of fish conservation.

Morphological analysis of the reproductive activity of Curimatella lepidura (Characiformes: Curimatidae).

Curimatella lepidura, commonly known as the manjuba, belongs to the Curimatidae family. To assess the reproductive activity of this species, fish were collected from three sections of the São Francisco River: section 1 = the Três Marias reservoir (TMR), section 2 = the SFR immediately downstream of the TMR, and section 3 = the SFR 54 km downstream from the TMR after the confluence of the SFR with the Abaeté River. Fish were collected bimonthly from January to December 2012. From this, the gonadosomatic index (GSI), Fulton condition factor (K), gonadal maturation stages in females and males, and diameters of vitellogenic follicles were determined. That is, this study employed histological and histometrical techniques to study the ovaries and testes of collected fish. The Fulton condition factor was statistically higher in section 1 than in the other sections, indicating that C. lepidura presents better health conditions in this section. Fish in the maturation/mature gonadal stage were collected in the November/December and January/February bimesters, coinciding with high temperatures, a long photoperiod, and abundant rainfall in this region. The mean vitellogenic follicle diameter was statistically lowest for sections 2 and 3, with a better impact on reproduction than in section 1. Overall, the results show that C. lepidura has reproductive success in lentic environments, such as in section 1, the TMR.

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.

Exposure to acetaminophen impairs gametogenesis and fertility in zebrafish (Danio rerio).

Acetaminophen (ACE; paracetamol) is one of the most widely used nonsteroidal anti-inflammatory drugs worldwide and is often found in aquatic systems, where it can act on nontarget species and impair fish reproduction. This study aimed to investigate the effects of chronic exposure to environmentally relevant ACE concentrations (0.5, 5 and 50 µg/L) on multiple reproductive parameters in zebrafish (Danio rerio). Gametogenesis was analyzed using histology, morphometry, cell proliferation, and apoptosis. This study also evaluated sex steroids, and prostaglandin E2 (PGE2) levels, gene expression for sex steroids and PGE2 receptors, fertilization rate, and semen quality. In females, exposure to 5 and 50 µg/L ACE induced larger and more abundant vitellogenic follicles and increased follicular atresia. In these treatments, males showed a lower proportion and proliferation of undifferentiated spermatogonia and a higher proportion of TUNEL-positive differentiated spermatogonia, spermatids, and spermatozoa, resulting in lower sperm production. ACE increased 17ß-estradiol (E2) and reduced 11-ketotestosterone levels in the testis, whereas only E2 increased in the ovaries. In both sexes, gonadal PGE2 levels were reduced. ACE at 50 µg/L induced an increase in the gene expression of androgen, estrogen, and PGE2 receptors in the ovaries, and reduced expression in the testes. Results also showed lower egg production and fertilization rate from 28 days of exposure with reduced sperm quality. These results demonstrated that ACE impairs the reproductive performance of zebrafish, affecting multiple reproductive parameters, which may be caused by the synergistic action of the imbalance of sex steroids, with a reduction of PGE2 and its receptors.

Effects of temperature manipulation on gamete development and reproductive activity in the farmed catfish Lophiosilurus alexandri.

Temperature is a critical factor for fish management, especially during breeding season. This study evaluated gametogenesis and gonadal maturation in the catfish Lophiosilurus alexandri under farming conditions in two temperatures. The fish were divided in the following experimental groups: (S0) control group, before starting the experiment, (S1) 30 days at 23 °C, (S2) 70 days at 23 °C, (S3) 30 days at 27 °C, and (S4) 70 days at 27 °C. Gonad, liver, and blood samples were obtained to analyze reproductive and health parameters. In females, increased gonadosomatic index (GSI) was associated with a decreased proportion of perinucleolar follicles and increased diameter of vitellogenic follicles in S4. Postovulatory follicles were found only in fish kept at 27 °C, whereas atretic follicles were more frequent at 23 °C. In S4, females had higher hepatic levels of vitellogenin and lower levels of zona radiata proteins. In males, a lower proportion of spermatogonia was found at 27 °C (S4), whereas GSI and proportions of spermatocytes, spermatids, and spermatozoa were similar among the groups. Levels of cortisol were higher in females of group S3. Plasma 17ß-estradiol, 11-ketotestosterone and 17α-hydroxyprogesterone were significantly higher in S4. Hematocrit, erythrocytes, and glucose were higher at 27 °C. Together, the present study indicate that exposure of L. alexandri to 27 °C provides suitable conditions for germ cell development and gonadal maturation in captivity, promotes increase of sex steroids, follicular growth, and oocyte maturation, with onset of ovulation occurring at 30 days. At 23 °C, spermatogonia proliferation is favored in males, but it cannot be recommended for stimulating female maturation of L. alexandri in fish farming.

Adverse effects of herbicides in freshwater Neotropical fish: A review.

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.

Morphological analysis of Prochilodus argenteus ovaries in successful and unsuccessful hypophysation-induced reproduction.

Pampus argenteus is a species of economic importance for professional fishing and aquaculture. To analyse the quality of oocytes of P. argenteus, 10 females were kept in tanks of 200 m2 with an average depth of 1 m in the Integrated Center of Fishing Resources and Aquaculture of Três Marias - CODEVASF. Specimens were submitted to hypophysation-induced reproduction with crude extract of common carp pituitary (EBHC). Females received two doses (0.8-1.0 and 5.0-6.6 mg of EBHC/kg body weight, respectively), with a 12-h interval between doses. For males, a single dose (2.7 mg/kg body weight) was applied at the same time as the females' second dose. Oocytes were extruded manually 8 h after the second hormonal dose at 26°C. It was observed that seven females responded positively to the procedure while the other three released bloody and lumpy oocytes. For histological analysis, ovarian fragments were fixed in Bouin's liquid for 8-12 h and submitted to routine histological techniques. The protocol was considered successful for 70% of females and 100% of males. The fertilization rate of the females from the unsuccessful group was very low, and histological analyses showed that most of their oocytes were in follicular atresia, suggesting a delay in hormonal administration or extrusion could have occurred. Despite the hypophysation protocol being considered adequate for the induced reproduction of P. argenteus, complementary studies are necessary to evaluate the possible causes of this degenerative process.

Reproduction of saguiru Steindachnerina elegans (Steindachner, 1874) (Pisces: Curimatidae) in the São Francisco River, downstream from a large reservoir in south-eastern Brazil.

The gametogenesis and reproduction of S. elegans from the São Francisco River at Três Marias, Minas Gerais, were analyzed in this study. Steindachrina elegans is a species abundant in the São Francisco River basin and an important fish in the food chain. The size at first gonadal maturation (indicated by the total length of the shortest spermatid male and spawned female) was 10.5 cm and 15.0 cm, respectively. Reproduction occurred more frequently from September to April. This period had high water temperature values. A high frequency of females was observed at the mature and spawned stages and height gonadosomatic index (GSI). Meanwhile, in males, the reproductive peak was from November to February. The long spawning period and the histological characteristics of the spawned ovaries that contained oocytes at different stages of development along with post-ovulatory and atretic oocytes indicates that the spawning of S. elegans is of the partial type.

Biomarker responses induced by bisphenol A on spermatogenesis in a Neotropical teleost fish are temperature-dependent.

Bisphenol A (BPA) is an organic synthetic compound used in the plastic industry with endocrine disrupting activity. Although it is frequently found in surface waters, few studies have investigated its impact on fish gametogenesis, particularly when associated with natural stressors. In this regard, the present study evaluated BPA toxicity on spermatogenesis in the lambari Astyanax bimaculatus under controlled conditions and its interactive effects with water temperature. Adult specimens were exposed in duplicate to 40 µg/L and 400 µg/L BPA at 23 °C and 28 °C for 21 days; the control group did not receive BPA. Testicular samples were collected and analyzed using different cellular and molecular techniques. The results showed a significant reduction in the gonadosomatic index in the BPA-treated groups at both temperatures. A decrease in the testicular levels of 11-ketotestosterone was observed in the 400 µg/L BPA group at 23 °C, 17ß-estradiol increased significantly in the treated groups at 28 °C, and vitellogenin showed no difference between the treatments. The morphometric analysis of spermatogenesis revealed a significant increase in the proportion of spermatogonia, spermatocytes, and Sertoli cells in the treated groups, with a higher proportion at 23 °C than at 28 °C. Otherwise, the proportion of spermatozoa was significantly lower in the BPA-treated groups, with a greater reduction at 23 °C. In addition, BPA also stimulated spermatogonial proliferation in the treated groups, but apoptosis was significantly increased in spermatids at 23 °C. Testis-ova, cell degeneration, and chromatin alterations in spermatids and Sertoli cells were observed in the germinal epithelium of the BPA-treated groups. The integrated biomarker response (IBR) index revealed that the analyzed endpoints are suitable for assessing estrogenic contamination. Taken together, our results indicate that the interactive effects of BPA and temperature contribute to the impairment of spermatogenesis in A. bimaculatus with more severe effects observed on sperm production at 23 °C than at 28 °C.

Evaluation of the oestrogenic potential of oestrone and bisphenol-A on the reproduction of Astyanax bimaculatus males after subacute exposure.

In the last decades, oestrogenic compounds have often been reported in environmentally relevant concentrations in aquatic environments around the world. Most laboratory studies of oestrogens try to understand the effects of a single contaminant, but in natural environments, the effects may be quite different due to interactions with other compounds. The present study aimed to compare the action of oestrone (E1) and bisphenol-A (BPA), acting singularly and in combination, on the spermatogenesis of Astyanax bimaculatus. After exposure to 100 ng/L of E1, BPA and a mixture of the two for 15 days, our results showed that E1 and the E1 + BPA mixture significantly altered the number of spermatogenic cells. BPA presented high cytotoxicity when compared to other treatments. Analysis of the two oestrogenic compounds suggests that the E1 + BPA mixture has no additive or synergistic effects. Together, the results of the present study indicate that endocrine-disrupting chemicals (EDCs) analysed alone may behave differently than when administered with other substances.

Induced reproduction and early development in dourado, Salminus franciscanus Lima & Britski, 2007 (Pisces: Characiformes).

Our study aimed to establish the response of Salminus franciscanus to hypophysation and describe the main morphological events of its embryonic process. Wild fish were captured in São Francisco River and selected broodstock (females: 66.4 ± 11.1 cm and 4.04 ± 2.32 kg; males: 58.3 ± 10.2 cm and 3.62 ± 1.12 kg) were kept at 26.1 ± 0.6°C for induction of final maturation/gamete release via the hypophysation technique. In females, two doses (0.8 and 5.6 mg/kg body weight) of crude pituitary extract of common carp (Cyprinus carpio) were administered with a 14 h interval. For males, a single dose (2.7 mg/kg body weight) of crude pituitary extract was applied at the same time as the females' second dose. Oocytes and sperm were manually stripped 8 h after a females' second hormonal dose. Fertilization was carried out using the dry method. Eggs were kept in funnel-type 60 L incubators at 24.3 ± 0.3°C and were analyzed and photographed every 10 min. After hormonal induction, 60% of females and 100% of males reacted positively and no broodstock mortality was recorded. The females released an average of 385.2 ± 78.4 g of oocytes and the fertilization rate observed was 50.4 ± 12.3%. The blastopore closure occurred at 7.5 h, somite formation at 12 h and hatching at 20 h post-fertilization. In general, the results of this study improve the understanding of the reproductive biology of dourado and confirm its potential for fish farming in the neotropical region.

Metapopulation dynamics of the migratory fish Prochilodus lineatus (Characiformes: Prochilodontidae) in a lotic remnant of the Grande River, Southeastern Brazil

River impoundments for electricity generation lead to environmental changes which severely affect fish migration and species richness. However, little is known about their effect on the genetic structure and population dynamics downstream from the reservoir. Here, we analyzed a set of ten microsatellite loci of Prochilodus lineatus, an important South American migratory fish. Specimens (n = 150) were sampled from five sites in a remnant lotic system that includes sections of the Grande, Pardo and Mogi Guaçu rivers, southeastern Brazil. The data showed that all microsatellites were polymorphic with the allele number per locus ranging from 5 to 32, and genetic diversity (H e ) varied from 0.74 to 0.80. Indices of genetic differentiation and Bayesian analysis showed a significant genetic structure and three genetic clusters inhabiting this river system. An asymmetric gene flow suggests source-sink metapopulation dynamics from tributaries (genetic source) to the main river (genetic sink). A genetic cluster that was not detected in the upper Mogi and Pardo rivers tributaries may indicate there is a "trapped gene pool" downstream from the Porto Colômbia dam. Thus, here we provide new insights into the genetic structure and population dynamics of a migratory fish species in a highly dammed river basin.(AU)

Represamento de rios para geração de eletricidade levam a mudanças ambientais que afetam severamente a migração de peixes e riqueza de espécies. No entanto, pouco se sabe sobre seu efeito na estrutura genética e dinâmica populacional a jusante de reservatórios. Aqui, analisamos um conjunto de dez loci de microssatélites de Prochilodus lineatus, um importante peixe migratório sul-americano. Os espécimes (n = 150) foram amostrados em cinco locais de um sistema lótico remanescente que inclui seções dos rios Grande, Pardo e Mogi Guaçu, sudeste do Brasil. Os dados mostraram que todos microssatélites eram polimórficos com o número de alelos por locus variando de 5 a 32 e diversidade genética (H e ) variou de 0,74 a 0,80. Índices de diferenciação genética e análise de agrupamento baseada em modelo bayesiano indicou a presença de três agrupamentos genéticos habitando este sistema fluvial. Um fluxo gênico assimétrico sugere dinâmica metapopulacional de fonte-sumidouro dos tributários (fonte genética) para o rio principal (sumidouro genético). Um agrupamento genético que não foi detectado nos tributários rio Mogi e rio Pardo parecem indicar que há um "trapped gene pool" a jusante da represa de Porto Colômbia. Assim, nós provemos aqui novos conhecimentos sobre a estrutura genética e dinâmica populacional de uma espécie de peixe migratório em um rio altamente fragmentado por barramentos.(AU)

Insulin-like growth factors 1 and 2 are associated with testicular germ cell proliferation and apoptosis during fish reproduction.

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.

Heavy metal contamination in a highly consumed Brazilian fish: immunohistochemical and histopathological assessments.

Due to industrial, rural, and domestic waste disposal, heavy metals such as cadmium (Cd), chromium (Cr), lead (Pb), zinc (Zn), copper (Cu), and iron (Fe) continually infiltrate aquatic environments. These pollutants do not degrade naturally and, thus, have a high capacity for bioaccumulation in tissues and organs. The present study uses histological and immunohistochemical analyses to evaluate the contamination status of Salminus franciscanus, a large and economically important fish. Levels of Cd, Cr, Pb, Zn, Cu, and Fe were evaluated by atomic absorption spectrometry in the liver and muscle of fish sampled from two tributaries of the upper São Francisco River Basin, Brazil: the Abaeté and Paraopeba Rivers. In addition, histopathological alterations and expressions of three environmental biomarkers were assessed: metallothionein (MT), heat shock protein-70 (HSP70), and cytochrome P450-1A (CYP1A). The results show that fish from the Paraopeba River are unsuitable for human consumption, with several metals being detected above the safe limits established by the World Health Organization. Histopathological alterations in the liver and spleen were also significantly more frequent in fish from the Paraopeba River than in those from the Abaeté River (P < 0.05). Significant differences in the expressions of environmental biomarkers were observed between the rivers. Fish from the Abaeté River presented significantly higher values of the gonadosomatic index (GSI) and lower levels of metal contamination in the liver and muscle.

Effects of metal contamination on liver in two fish species from a highly impacted neotropical river: A case study of the Fundão dam, Brazil.

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.

Reproductive variables of Brycon nattereri Günther, 1864 (Pisces: Characidae), an endangered commercial species.

In Brazil, fishing in continental waters is prohibited from November to February, the rainy season, when most commercially important fish species are reproductively active. Brycon nattereri is a native species to the Paraná, Tocantins, and São Francisco River basins in Brazil and is on the national list of species threatened with extinction. The goal of this study was to analyse the main reproductive variables of B. nattereri from the Lourenço Velho River, located in the Paraná River basin, south-eastern Brazil. From 2013-2016, 326 specimens (156 females and 170 males) were caught bimonthly using gill nets. Biometric data, gonadosomatic index (GSI), and fecundity were determined for each specimen. The gonadal maturation stages and the breeding season were established. There were relatively greater GSI values for males and average values were similar to those of females, an uncommon feature in Neotropical freshwater fish. The greatest frequencies of mature fish occurred from April to July in the dry season, which is when there are least ambient temperatures. The fecundity for body weight varied from 16,300 to 62,800 oocytes per female and fully developed vitellogenic oocytes had a mean diameter of 1175 ± 278.87 µm. These results indicate that B. nattereri breeds in the dry season when the water temperature is colder and, therefore, protection from fishing of this species during this season needs to be established.