River In Southeastern Brazil Research Articles

Water level regime variation is a crucial driver for taxonomic, functional, and phylogenetic diversity in seasonally flooded tropical forests

Floodplains contribute significantly to terrestrial ecosystem service provision but are also among the most vulnerable and degraded ecosystems worldwide. Heterogeneity in floodplain properties arises from variations in river-specific flood regimes, watershed characteristics, and valley morphology, influencing seasonally flooded forests' taxonomic, functional, and phylogenetic diversity. This study addresses persisting knowledge gaps in floodplain ecology, focusing on the seasonally dry tropics. We explore the relationships between flood regime, environmental conditions, vegetation composition, functional and phylogenetic diversity, and the impact of environmental variables on above-ground biomass (AGB) and ecological strategies. The study spans six rivers in southeastern Brazil's main river basins: Rio Grande and São Francisco. We identified five eco-units in each floodplain based on flooding regimes and surveyed six plots per eco-unit. We measured trees with DBH > 5 cm and collected functional traits, along with detailed soil, climate, and water level data. We calculated plot-level floristic composition, taxonomic, functional, and phylogenetic diversity, wood density, and AGB. Functional and phylogenetic dissimilarity were analyzed, and the effects of climate, soil, and hydrological variables were quantified using generalized linear mixed models. We show how flood frequency and duration affect floristic composition across the floodplains. Taxonomic and phylogenetic diversity responded to climate, soil, and hydrological variables, while functional diversity responded primarily to hydrological variables, emphasizing the role of environmental filtering. Hydrological seasonality, soil fertility, and flood regime emerged as key factors shaping community structure and ecological strategies in the studied seasonally flooded tropical forests. Plot-level AGB responded to phosphorus but not to climate or hydrological variables. The study also highlights functional and phylogenetic dissimilarities among eco-units and basins, indicating potential climate change impacts.

Metal-contaminated sediment toxicity in a highly impacted Neotropical river: Insights from zebrafish embryo toxicity assays

The Fundão dam collapse was one of the largest mining-related disasters globally. It resulted in the release of mining tailings containing heavy metals, which contaminated the Doce River in southeastern Brazil. This study assessed the effects of acute exposure of Danio rerio embryos to sediments contaminated by mine tailings six years after the Fundão dam collapse. The study sites included P2, P3, and P4 in the upper Doce River, as well as site P1 on the Piranga River, an uncontaminated river. Sediment samples were analyzed for 10 metals/metalloid by atomic absorption spectrometry. In the assays, embryos were exposed to sediment from P1–P4 sites, and uncontaminated quartz was used as control sediment. Various biomarkers were applied to assess biological responses, and the integrated biomarker response (IBR) index was calculated for each site. Sediment samples revealed elevated levels of As, Cr, Cu, Hg, and Ni beyond Brazilian legislation limits. At 96-h exposure, embryo mortality rates exceeded 20% in P1, P2, and P3, higher than the control and P4 (p < 0.0001). Hatching rates ranged from 60 to 80% in P1, P2, and P3, lower than the control and P4 (p < 0.001). Larvae exposed to P2 sediment (closest to the Fundão dam) exhibited skeletal, physiological, and sensory malformations. Neurotoxicity was indicated by increased acetylcholinesterase activity and reduced spontaneous movements in embryos exposed to Doce River sediment. Contamination also increased metallothionein and heat shock protein 70 levels, along with changes in cell proliferation and apoptosis. Principal component analysis showed a good correlation between metals/metalloid in the sediment and larval morphometric endpoints. The IBR index highlighted suitable biomarkers for monitoring metal contamination in fish embryos. Overall, our findings suggest that sediment toxicity following the Fundão dam failure may compromise the sustainability of fish communities in the Doce River.

Gold single-grain microCT scanning: operational constraints and first results in Brazilian alluvial grains

ABSTRACT The present work sought to investigate the applicability of the microCT scanning beyond petrophysics in oil and gas industry. We analysed external features (morphology) with all their nuances, and internal features such as mineral inclusions and vugs, in micrometric alluvial gold grains from one of the largest rivers in Southeastern Brazil. Owing to the complicated X-ray interactions with any metallic material, mainly gold, several imaging protocols were used until obtaining the most appropriate one. The results corroborate that microCT scanning can be a useful tool in provenance studies of detrital gold grains, even in an adverse analytical context and with small gold grain populations.

Microplastics in water from the confluence of tropical rivers: Overall review and a case study in Paraiba do Sul River basin

Rivers are known for carrying out a fundamental role in the transportation of human debris from continental areas to the marine environment and have been identified as hotspots for plastic pollution. We characterized microplastics (MPs) along confluence areas in the Paraíba do Sul River basin, the biggest river in southeastern Brazil. This water body crosses highly industrialized areas, with the highest population density, and the major water demand in South America. Considering the important ecological function of this extensive watershed and the implications of MP pollution, we evaluate the spatial variation of MP concentration in the confluence areas and upstream from the confluence. Samples were taken from the superficial layer of the water column in February and June 2022, using manta net with 300 μm mesh size. A total of 19 categories and 2870 plastic particles were determined. The confluences areas of rivers showed the highest concentration of MPs, highlighting the confluences of the Paraiba do Sul and Muriaé rivers (0.71 ± 0.25 MP/m3), followed by Paraíba do Sul and Dois Rios rivers (0.42 ± 0.23 MP/m3) and Paraíba do Sul and Pomba rivers (0.38 ± 0.14 MP/m3). Black fibers were the main category, followed by blue fibers and blue fragments. The MPs in the surface waters of Paraíba do Sul River is significantly influenced by the sampling points spatiality. This result corroborates other studies around the world and reinforces the argument that affluents are important sources for the introduction of MPs in larger rivers. Nevertheless, our results provide a better understanding of the different contributing factors and occurrence of MPs in river basins.

Do mismatched genitalia promote mechanical isolation in syntopic species of Phalloceros fishes (Poeciliidae)?

Abstract The elucidation of mechanisms responsible for the reproductive isolation of species is a fundamental part of speciation research. South American poeciliid fishes in the genus Phalloceros represent a promising system in which to study the evolution of reproductive barriers between closely related species. Phalloceros are often found in sympatry with non-sister congeners, and most such species pairs have morphologically divergent female and male genitalia. In recent studies, it has been hypothesized that mismatched genitalia between co-occurring Phalloceros species might act as mechanical barriers to prevent hybridization and might help to explain the diversification of this group. However, this idea has not yet been evaluated empirically with genetic data. Here, we tested this hypothesis using morphological data in conjunction with mitochondrial and nuclear DNA sequence data. Our study focused on Phalloceros anisophallos and Phalloceros leptokeras, two non-sister species that have mismatched genitalia and that occur together in at least four rivers in south-eastern Brazil. Despite the prevalence of hybridization between closely related non-sister species of animals, especially fish, our phylogenetically-based results detected no evidence of mitonuclear discordance and (hence historical hybridization) between the two focal species. Our findings are therefore consistent with the hypothesis that mismatched genitalia prevent hybridization between sympatric species of Phalloceros fishes.

Bioaccumulation and health risk assessment of trace metal contamination in the musculature of the trahira fish (Hoplias malabaricus) from two neotropical rivers in southeastern Brazil

BackgroundFish are an important source of nutrition for humans. Artisanal fishing plays a fundamental role in Brazil fish production. In Brazil, the unrestrained increase, diffusion, and little importance for environmental causes of other economic activities, such as the agricultural industry, has caused irreparable damage, leading to the contamination of water bodies. Among the countless pollutants that reach water bodies, trace metals are extremely problematic. Here, we evaluated the bioaccumulation and health risk of trace metal contamination in the musculature of the trahira fish (Hoplias malabaricus), collected from two rivers in southeastern Brazil. MethodsDuring the period from May 2017 to November 2019, 90 fish were collected, 45 from each river. River water samples were also taken during the same collection periods. From fish, muscle tissue samples were taken, and together with river water samples, analyzed for the recovery of trace metals (Al, Cr, Mn, Fe, Ni, Cu, As, Cd, and Pb) through the technique of Inductively Coupled Plasma Mass Spectrometry (ICP-MS). ResultsIn general, fish as well as the waters of the Jacaré-Guaçú River had higher concentrations of metals. The elements Al, Cr and Cd stood out from the others analyzed metals for having a hazard index (HQ) above 1 (Al), for being up to 10 times above the concentrations allowed by Brazilian legislation (Cr) and for having a high bioconcentration factor (Cd), indicating a biomagnification process through the food chain. ConclusionIn general, trace metal concentrations in the waters and fish of the Jacaré‐Guaçú were higher than in the Jacaré-Pepira, which shows that the Jacaré‐Guaçú is the one that suffers more anthropogenic action between the two rivers. In addition, some elements such as Al, Cr and Cd, due to its high concentrations, should receive some attention as they can pose risks to the health of fish, which can jeopardize the survival of their populations, and especially to humans who use these animals as a food source.

Macronutrients and dissolved iron in a land-ocean approach: Influences of contamination by ore tailings in Southeastern Brazil

Recently, many dam rupture disasters related to the mining industry have caused significant disruption to ecosystems globally. Contaminants, including nutrients in excess, can be transported from the river watersheds to the ocean in great quantities. In 2015, millions of m3 of iron ore tailings were released in the Doce River in southeastern Brazil, leading to several damaging effects to the river and marine ecosystem. So far, few studies have integrated the impact of these tailings on the river and the sea simultaneously. This research aims to provide a perspective on the macronutrients and iron concentrations and balance in the Doce River and the adjacent continental shelf, the related abiotic factors and the phytoplankton response under a new steady state of iron enrichment environment. The iron ore tailings increased the concentrations of nutrients in the river and on the continental shelf, especially for dissolved silica and iron. There was also a long-term indirect phosphorus enrichment associated to adsorption/desorption onto Fe-oxides and a nitrogen increase possibly due to N-fixing enhanced by iron. N fixation/remineralization predominates in the river watershed, while in the sea, the hydrodynamics provides nutrients supplied by the river and recycling from sediment resuspension. Nutrient ratios show DIP limitation in the river, while the complex marine environment brings both limitations on DIN, DIP, and DSi, as well as a stoichiometric equilibrium to the dataset. The phytoplankton response to the abiotic factors was more representative in the river watershed than on the continental shelf. This work emphasizes the importance of reporting local data for understanding global land-ocean nutrient fluxes and their potential influence on primary productivity and trophic chain balance.

Spatiotemporal Discharge Variability of the Doce River in SE Brazil During MIS 6 and 5

The modern precipitation balance in southeastern (SE) Brazil is regulated by the South American summer Monsoon and threatened by global climate change. On glacial-interglacial timescales, monsoon intensity was strongly controlled by precession-forced changes in insolation. To date, relatively little is known about the spatiotemporal distribution of tropical precipitation in SE Brazil and the resulting variability of fluvial discharge on glacial-interglacial timescales. Here, we present X-ray diffraction-derived mineralogical data for the 150–70 ka period (marine isotope stage (MIS) 6 to MIS 5) from the Doce River basin. This area was sensitive to changes in monsoonal precipitation intensity due to its proximity to the South Atlantic Convergence Zone. The data, obtained from a marine sediment core (M125-55–7) close to the Doce river mouth (20°S), show pronounced changes in the Doce River suspension load’s mineralogical composition on glacial-interglacial and precessional timescales. While the ratio of silicates to carbonates displays precession-paced changes, the mineralogical composition of the carbonate-free fraction discriminates between two assemblages which strongly vary between glacial and interglacial time scales, with precession-forced variability only visible in MIS 5. The first assemblage, dominated by high contents of kaolinite and gibbsite, indicates intensified lowland erosion of mature tropical soils. The second one, characterized by higher contents of the well-ordered illite, quartz and albite, points to intensified erosion of immature soils in the upper Doce Basin. High kaolinite contents in the silicate fraction prevailed in late MIS 6 and indicate pronounced lowland soil erosion along a steepened topographic gradient. The illite-rich mineral assemblage was more abundant in MIS 5, particularly during times of high austral summer insolation, indicating strong monsoonal rainfall and intense physical erosion in the upper catchment. When the summer monsoon weakened in times of lower insolation, the mineral assemblage was dominated by kaolinite again, indicative of lower precipitation and runoff in the upper catchment and dominant lowland erosion.

The Influence of Natural Barriers on the Amphidromous Shrimp Potimirim brasiliana (Caridea, Atyidae) from Two Rivers in Southeastern Brazil.

AbstractThe migratory behavior of freshwater shrimps may be affected by natural barriers in limnetic environments. This study evaluated the river areas separated by natural barriers, such as waterfalls, which affect the amphidromous shrimps' (Potimirim brasiliana) population features and reproductive aspects. Results indicate that in the Félix and Prumirim Rivers from southeastern Brazil shrimps show few differences in sampling areas, and these differences may not be causally related to the waterfalls. This is demonstrated by the absence of a pattern in the size and sex ratio in each area and the absence of a significant difference in most reproductive aspects. The presence of juveniles and reproductive individuals in all sampling areas strongly indicates a constant migration along them in both rivers, indicating that all individuals evaluated correspond to one single patchy population structure for each river. This migration conducted by P. brasiliana, such as its crawling behavior, demonstrated that it would be important to maintain the minimum number of individuals flowing between the different river sampling areas in this shrimp group. Thus, based on a helpful model observed in P. brasiliana, the results help us understand how natural barriers may affect the populations of amphidromous shrimp and how the migration behavior up- and downstream can help sustain the population. This premise can help future construction decisions and impacts of unnatural barriers, such as dams.

Evolution of the Semideciduous-Riparian Forest (ecotone Cerrado-Atlantic Forest) during the late Holocene, Southeast of Brazil

The floodplains of meandering rivers in southeastern Brazil represent places where the sedimentary record associated with the history of transition/ecotone areas and exchange of biomes accumulates, such as the Cerrado (Cerradão Forest) and Atlantic Forest (Semideciduous-Riparian Forest). The present study aims to use palynological, isotopic (δ13C, δ15N and 14C), and anthracological indicators in cores taken from three abandoned meander bends to make inferences about environmental evolution, vegetation reconstruction, and climatic inferences. The study area is located in the Mogi Guaçu River Basin, in the countryside of São Paulo State. The studies show that ~2,730 BP (stage I), the area underwent through a more humid climatic phase compared to the current one, which allowed the expansion of the Riparian Semideciduous Forest. After that date, in stage II (1,800 to 510 BP), the percentage of the Cerrado (Cerradão Forest) increased, due to a drier period. From 510 BP to the present day (stage III), humidity has taken place with a new expansion of the Riparian Semideciduous Forest, although elements of Cerrado are present. Microscopic charcoal fragments were found in all stages and may infer the incidence of paleo-wildfires during the Late Holocene. The results indicate that both phytophysiognomies remained for the studied period, varying their expansion depending on the humidity present in each stage. Although lakes formed by abandoned meanders are not areas with the best palynological record, they are frequent environments in the interior of the continents. If properly interpreted, they may provide relevant information to vegetation and climatic changes for the areas. Keywords: paleoenvironmental studies, Holocene, river dynamics, pollen grains, isotopic analysis, charcoal fragments.

AQUATIC MACROPHYTES DIVERSITY IN THE LOWER DOCE RIVER BASIN, ESPÍRITO SANTO, BRAZIL

Macrophytes are plant organisms that live partially or totally submerged in water, being fixed and free. The Doce River is one of the main rivers in southeastern Brazil and, in 2015, it was hit by ore tailings from the Fundão dam burst in Mariana, Minas Gerais. This work aims to provide a floristic survey of macrophytes in the lower Doce River basin and to compare the species composition between lentic and lotic environments. Expeditions were carried out monthly from October 2018 to September 2019, in five stations in lotic and six in lentic environments. A total of 105 species belonging to 33 families of vascular plants were recorded, among them 14 are new occurrences for Espírito Santo state. Richest families were Poaceae (23 spp.) and Cyperaceae (22 spp.). Amphibious/emerging plants were the most representative (46 spp.). NMDS analysis revealed that the composition of the lotic and lentic environments are different.

Fishers’ knowledge on the ecology, impacts and benefits of the non-native peacock bass Cichla kelberi in a coastal river in southeastern Brazil

Ethnoichthyology has been used to understand how humans perceive environmental changes, including species introductions. In Rio de Janeiro State, southeastern Brazil, fishers introduced juveniles of peacock bass Cichla kelberi in the Juturnaiba Reservoir in the 1990’s. In the last years, this fish started to be caught in the Sao Joao River, downstream of the dam. This study aimed to identify whether fishers recognize the potential impact of the peacock bass over the native species, to understand the economic valuation they made to the services provided by this species, and if they include management of the non-native peacock bass in their practices. Semi-structured interviews with artisanal and sport fishers were employed between September and October 2016. A total of twenty-five interviews were carried out, 12 with artisanal and 13 with sport fishers. In general, fishers expressed knowledge about biological and behavioral aspects of the peacock bass, but opinions diverged on its impact over the native ichthyofauna. Differently from the artisanal, most sport fishers do not relate the decline in the population of other native species to the occurrence of the peacock bass. Instead, they mention other anthropogenic impacts in the Sao Joao River basin. The later advocate the practice of fish and release for the peacock bass, in order to maintain their population in the study area. The ethnoichthyological knowledge gathered from fishers provide novel information related to the native ichthyofauna, peacock bass introduction and other anthropogenic impacts, and might constitute a powerful tool to the development of sustainable strategies.

Shifts in bacterial communities and antibiotic resistance genes in surface water and gut microbiota of guppies (Poecilia reticulata) in the upper Rio Uberabinha, Brazil

Anthropogenic activities especially water pollution can affect the diversity and composition of microbial communities and promote the spread of antibiotic resistance genes (ARGs). In this study, water samples and guppies (Poecilia reticulata) were sampled from six sampling sites along the Uberabinha River in southeastern Brazil, both microbial communities and ARGs of surface waters and intestinal microbiota of guppies (Poecilia reticulata) were detected. According to the results of 16S rRNA amplicon sequencing, Proteobacteria, Bacteroidetes, Firmicutes and Actinobacteria were dominant phyla in both water and intestinal microbiota, but the abundance of putative pathogens was higher at heavily polluted sites. Up to 83% of bacteria in intestinal microbiota originated from water microbiota; this proportion was relatively higher in less polluted compared to polluted environments. ARGs providing resistance of tetracyclines and quinolones were dominant in both water and gut microbiota. The relative abundances of class I integrons and ARGs were as high as 1.74 × 10−1/16S rRNA copies and 3.61 × 10−1/16S rRNA copies, respectively, at heavily polluted sites. Correlation analysis suggests that integrons and bacteria play key roles in explaining the widespread occurrence of ARGs in the surface, but not in intestinal microbiota. We could rule out the class I integrons a potential intermediary bridge for ARGs between both types of microbiomes. Our results highlight the tight link in microbial communities and ARGs between ambient microbiota of stream ecosystems and intestinal microbiota of fish. Our study could have far-reaching consequences for fisheries and consumer safety and calls for investigations of gut microbiota of target species of both commercial fisheries and recreational (hobby) angling.

Fishers' knowledge on the ecology, impacts and benefits of the non-native peacock bass &lt;i&gt;Cichla kelberi&lt;/i&gt; in a coastal river in southeastern Brazil

Ethnoichthyology has been used to understand how humans perceive environmental changes, including species introductions. In Rio de Janeiro State, southeastern Brazil, fishers introduced juveniles of peacock bass Cichla kelberi in the Juturnaíba Reservoir in the 1990’s. In the last years, this fish started to be caught in the São João River, downstream of the dam. This study aimed to identify whether fishers recognize the potential impact of the peacock bass over the native species, to understand the economic valuation they made to the services provided by this species, and if they include management of the non-native peacock bass in their practices. Semi-structured interviews with artisanal and sport fishers were employed between September and October 2016. A total of twenty-five interviews were carried out, 12 with artisanal and 13 with sport fishers. In general, fishers expressed knowledge about biological and behavioral aspects of the peacock bass, but opinions diverged on its impact over the native ichthyofauna. Differently from the artisanal, most sport fishers do not relate the decline in the population of other native species to the occurrence of the peacock bass. Instead, they mention other anthropogenic impacts in the São João River basin. The later advocate the practice of fish and release for the peacock bass, in order to maintain their population in the study area. The ethnoichthyological knowledge gathered from fishers provide novel information related to the native ichthyofauna, peacock bass introduction and other anthropogenic impacts, and might constitute a powerful tool to the development of sustainable strategies.

Patterns of distribution and accumulation of trace metals in Hysterothylacium sp. (Nematoda), Phyllodistomum sp. (Digenea) and in its fish host Hoplias malabaricus, from two neotropical rivers in southeastern Brazil.

Here we evaluated the potential for trace metal accumulation of two parasitic species, Hysterothylacium sp. (Nematoda) and Phyllodistomum sp. (Digenea), found parasitizing Hoplias malabaricus, a characiform fish also known as trahira, collected from two neotropical rivers, Jacaré-Pepira and Jacaré-Guaçú, in southeastern Brazil. Fish were collected between July 2017 and July 2019, totaling 90 fish specimens analyzed, 45 from each river. From fish, we take samples of three different tissues: muscle, intestine and liver. Along with the parasite samples taken from fish hosts, tissue samples were analyzed by an Inductively Coupled Plasma Mass Spectrometer (ICP-MS) for obtaining the trace metal (Al, Cr, Mn, Fe, Ni, Cu, As, Cd e Pb) concentrations. All elements were found in statistically higher concentrations in the parasites, both nematodes and digeneans, than in the host tissues, but in comparison, was observed that Hysterothylacium sp. had higher concentrations than those obtained in Phyllodistomum sp. We also found that uninfected fish had statistically higher concentrations of metals than infected ones. And in those who are infected, the size of the parasitic infrapopulations correlated negatively with the concentrations of trace metals obtained in the hosts tissues, that is, the concentrations in fish showed a tendency to decrease as the parasitic infrapopulations increased, or vice versa. In addition, our results show that the influence of the parasitic infrapopulations on metal concentrations in the fish host is not affected in cases of mono-infection or co-infection.

Late Pleistocene-Holocene landscape evolution in the lower Peixe river, Brazil: A meandering river valley

This study investigated the lower terrace and floodplain formation in the lower Peixe River in southeastern Brazil. Morphologic, sedimentologic and geochronologic analyses in this meandering tributary of the Paraná River allowed an integrated approach to reconstructing fluvial changes from the late Pleistocene. Geomorphic units were mapped with Global Navigation Satellite System, satellite imagery and digital surface model interpretation, and sedimentary facies and radiocarbon (14C) dating analyses were performed on palaeochannels and backswamps. The palaeochannels on the lower terrace indicate fluvial activity during the late Pleistocene, torrential flows during the Northgrippian stage, and abandonments during the Meghalayan stage. The backswamp evaluated on the lower terrace documents the depositional change from oxbow lake abandonment in the Greenlandian stage to tributary flow, which passes flows over the palaeodrainage during flood episodes, while another backswamp in the floodplain highlights an intense morphodynamic removal of terrace deposits. An incisive phase during the Meghalayan stage is the main event responsible for establishing the current fluvial landscape, which promotes the formation of the lower terrace and floodplain. Local variations (i.e., tributary flows) in the degradation process on the terraces results in a topographical and morphological contrast between corresponding geochronologic units. Therefore, adjustment stages in the fluvial relief drive wetland variability in the fill terraces, which are fundamental to understanding degradational processes and formulating environmental management policies.

Influences of small hydroelectric power plants on homogenization of the ichthyofauna in a tropical river

The native fishes of the Neotropical region have been heavily impacted by the construction of reservoirs that block the rivers in different degrees. Small Hydroelectric Power Plants (SHPP) have been an alternative way to take advantage of small electricity production potential, with low cost. However, there is no basis in the belief that SHPP have less deleterious effects on river habitat than large hydropower plants. The aim of this study was to evaluate eventual changes in the ichthyofauna because of the influences of SHPP in the middle reaches of a tropical river in south-eastern Brazil. The raised hypothesis is that SHPP change the ichthyofauna composition and increase the taxonomic and functional similarities (homogenization). Fish collections were carried out quarterly at six locations along a 20 km stretch of the Paraiba do Sul River, before and after the construction of the SHPP. The fish community structure changed between the two periods, with a decrease in the fish numerical abundance, whereas the species richness did not change. Sensitive species with specialized feeding habits (namely, Hartia loricariformis, Steindachineridium parahybae, Hypomasticus mormirops, Characidium alipioi, Chyphocharax gilbert, Corydoras nattereri and Pogonopoma parahybae) occurred only before the SHPP, being replaced by several species of Characiformes, among them four of genus Astyanax (namely, A. giton, A. hastatus, A. taeniatus, and A. intemedium) that are tolerant and omnivores; however, most of functional traits were maintained. The taxonomic dissimilarity increased significantly, whereas the functional dissimilarity did not differ between the two periods. The hypothesis of ichthyofauna homogenization was not confirmed in this study, probably because of the short time period since the SHPP construction.

Gonadal development and reproductive period of the characin Astyanax aff. bimaculatus (Characiformes: Characidae) in a tropical reservoir in southeastern Brazil

The gonadal development of the characin Astyanax aff. bimaculatus from Funil Reservoir, an impoundment in the middle reaches of the Paraiba do Sul River in southeastern Brazil was analysed through histological, histochemical and histometric techniques, and the spawning season was determined. Unbalanced sex ratio was found, with females outnumbering and reaching larger sizes than males. The following stages of oogenic cell development were identified for females: primary growth, pre-vitellogenic (cortical alveolar) and vitellogenic. In males, the following stages were determined: spermatogonia primary and secondary, spermatocyte primary and secondary, spermatid and spermatozoa. The spawning occurs most of the year, peaking in January-February, as indicated by the gonadosomatic index. In the peak of the spawning period, the condition factor and hepatosomatic indices decreased suggesting use of stored body energy reserves during the reproduction. Spawning in batches, small-sized oocytes and a long reproductive season suggest that Astyanax aff. bimaculatus fits to an opportunist strategy. Such strategy may facilitate the use of a wide range of lentic and lotic body waters in the Neotropical region.

&lt;b&gt;The use of biomarkers for assessing effects of pollutant stress on fish species from a tropical river in Southeastern Brazil

Biomarkers are measurements within an organism that respond to environmental effects and are used as tools in bioassessment programs since they reflect physiological changes induced by exposure to pollutants. The hepatosomatic index (HSI) and the condition factor (CF) in three fish species Geophagus brasiliensis, Hypostomus affinis and Hypostomus auroguttatus were used to assess effects of pollutant stress in a tropical river during two seasons (dry and wet). Fish from the least disturbed sites had the lowest condition factor (CF) and the lowest HSI, whereas those from sites near pollutant discharges had the highest CF and HSI. Higher HSI and lower CF occurred during the dry season. It is suggested that species adapted to stressful conditions take advantage on food availability from organic loads or unoccupied niches by lesser tolerant species, increasing CF. We concluded that higher HSI values were directly associated with environmental stress whereas the higher CF values are related to availability of food resources derived from organic loads or other sources. CF and HSI are simple and cost-effective, thus suitable as routine screening tools in pollution monitoring, but caution should be taken in relating changes in physiological measurements and any specific pollutant to prevent misinterpretation.

Organotropism of methylmercury in fish of the southeastern of Brazil

This is one of the first studies to evaluate the effect of biometric variables (total length and weight), diet, and abiotic matrices (sediment and water column) on the bioaccumulation of methylmercury in tissues (muscle, liver, and gills) of four fish (two carnivore-invertivores, Pimelodus fur and Pachyurus adspersus; one carnivore-piscivore, Oligosarcus hepsetus; and one omnivore, Pimelodella lateristriga) in the lower section of a river in southeastern Brazil. Samples of fish (n = 120), water (n = 5) and sediment (n = 5) were collected at five sites characterized by pollution with mercury due to the use of organomercury fungicides and stream bed gold mining, commonly carried out in that section of the river in the 1980s. The results show that biometric variables are strongly correlated with methylmercury levels in muscle (r = 0.61, p < 0.0005) of P. fur. As a rule, concentrations of total mercury and methylmercury did not vary considerably between the organs of the species of different food habits, because of the environmental conditions in the study area. Despite the low concentrations of mercury in sediments (<0.05 mg kg−1 wet. wt), this compartment is a representative source of this pollutant for the organisms investigated, due to the close contact these animals keep with it in view of the low water columns in that section of the river.