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We investigate the effects of spatial changes in environmental conditions and anthropogenic influences on larval fish communities in two tropical estuaries with varying levels of human impact. Our findings revealed a distinct structure of larval fish assemblages between the two estuaries located in northeastern Brazil, and we observed that eutrophication, characterized by high concentrations of nutrients, had adverse effects on the abundance and richness of larval fish assemblages. Additionally, we observed that a decrease in rainfall had an impact on larval fish assemblages, particularly during the dry season, when intermittent upstream rivers lead to changes in salinity and species composition within the estuaries. This study contributed to evaluating the community descriptors of two tropical estuaries under different levels of human influence, providing insights into the vulnerability of larval fish assemblages to climate change, specifically in relation to human influences and hypersalinity and the effects of marinization in shallow tropical estuaries in this region.

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Functional characteristics of species are of great importance for understanding their roles in ecosystems and can be used to detect long-term chances in the environment. We evaluated temporal changes (1983-1985 and 2017-2019) in taxonomic and functional indices of the fish fauna in shallow areas of a tropical bay heavily impacted by anthropogenic activities in recent decades. The hypothesis that functional indices change over time as a result of environmental degradation was tested. Our results showed a significant decrease in species richness and abundance over time, and in functional richness, while others functional diversity indices (divergency, evenness, and originality) remained stable. Thirteen functional groups were detected, some of which contained only one species, raising concerns about the loss of ecosystem functions due to ongoing changes. We also observed an increase in beta diversity over time, which may be the result of a decrease in local richness without leading to regional extinctions. Turnover was the most important process in structuring the fish fauna at the evaluated time scale. The relative stability of the functional structure and the higher levels of turnover seem to be related to the dominance of functional groups, within which species replace each other according to their responses to environmental filters that select for specific functional traits. Incorporating functional diversity indices and beta diversity variations in the fish community helped to enhance the existing information about this coastal system by offering improved estimates of biological diversity through diverse approaches. The predominance of turnover identified in the preset study suggests a dynamic and fluctuating species composition within the habitat. In this sense, habitat preservation should prioritize the protection of diverse habitats to accommodate a broad spectrum of species.

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The inshore area of the Southwestern Atlantic between 22 °S and 29 °S (South Brazilian Bight) is a transitional climatic zone, where the tropical and warm temperate provinces mix. In its northern part, i.e., in the coastal waters of Rio de Janeiro, Brazil, local oceanographic conditions, such as upwelling in the north, and great bays with different degrees of anthropogenic influences in the center and south can determine the population structure of several fish stocks. The Whitemouth croaker (Micropogonias furnieri) is one the most heavily exploited fishing resources in this area, but there are still some doubts about its population structure. In this study, through combined analyses using nuclear genetic markers and morphological and geochemical signatures of otoliths, a divergence of individuals between two populations was identified using microsatellites, while a finer spatial structure with three populations (north, center and south, respectively) was found based on otolith shapes and elemental signatures. This regional population structure may have direct implications for rational fisheries management and conservation of the species.

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Notholebias minimus is an endangered annual killifish endemic to the coastal plains of the State of Rio de Janeiro, Brazil. This study aimed to present new occurrences in the Atlantic Forest biome, provide unprecedented population features (body and egg size, fecundity, sexual ratio, and length-weight relationship - LWR), and compare changes in land use and coverage between 1985 and 2021 in biotopes located inside and outside protected areas. Three new occurrence localities were found in shallow temporary wetlands with acidic pH (6.4 ± 0.2) and low concentrations of dissolved oxygen (2.0 ± 0.9 mg/L). Males and females total length ranged from 11.1 to 31 mm and 11 to 26 mm, respectively. Batch fecundity ranged from 18 to 40 oocytes (24.8 ± 8.8), corresponding to oocytes with sizes between 800-1,006 µm (905 ± 56). Males were significantly larger than females (W = 2193.5, p = 0.0067), but both sexes occurred in similar proportions (p = 0.472). LWR showed positive allometry (b = 3.18). Biotopes located within protected areas exhibited higher conservation. Our discoveries expand the knowledge about habitat and population features of N. minimus and reinforce the importance of establishing protected areas for the conservation of annual fish biotopes.

Notholebias minimus é um peixe anual ameaçado de extinção, endêmico das planícies costeiras do Estado do Rio de Janeiro, Brasil. Neste estudo, objetivamos apresentar novas ocorrências no bioma Mata Atlântica, fornecer características populacionais inéditas (tamanho do corpo e dos ovos, fecundidade, proporção sexual e relação peso-comprimento), e comparar mudanças no uso e cobertura do solo entre 1985 e 2021 em biótopos localizados dentro e fora de unidades de conservação. Registramos três novos locais em áreas úmidas temporárias rasas com pH ácido (6,4 ± 0,2) e baixas concentrações de oxigênio dissolvido (2,0 ± 0,9 mg/L). O comprimento total de machos e fêmeas variou de 11,1 a 31 mm e de 11 a 26 mm, respectivamente. A fecundidade do lote variou entre 18-40 oócitos (24,8 ± 8,8), correspondendo a diâmetros entre 800-1.006 µm (905 ± 56). Os machos foram significativamente maiores que as fêmeas (W = 2193,5; p = 0,0067), mas ocorreram em proporções similares (p = 0,472). A relação peso-comprimento detectou alometria positiva (b = 3,18). Biótopos localizados dentro de áreas protegidas exibiram maior preservação ambiental. Nossas descobertas ampliam o conhecimento sobre as características do habitat e da população de N. minimus e reforçam a importância do estabelecimento de áreas protegidas para a conservação dos biótopos dos peixes anuais.

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Industrial wastewater and agricultural practices are among the main activities discharging organic pollutants, such as Polychlorinated biphenyl (PCB) congeners and organochlorine insecticides (e.g. DDT - dichloro diphenyl trichloroethane), to the environment. In this study, we used the native Cichlidae fish species Geophagus brasiliensis as a sentinel to evaluate the hepatic 7-ethoxyresorufin-O-deethylase EROD activity, a biomarker of exposure to CYP1A-inducing pollutants, to assess the bioavailability of xenobiotics in two reaches of a large lotic system in Southeast Brazil: a less disturbed area (site 1) in the upper stretch, and an area in the middle stretch, which receives various industrial and agricultural effluents from upstream cities (site 2). In addition, G. brasiliensis were exposed to a single dose of 50 mg kg-1 beta-naphthoflavone (BNF) or of 50 mg kg-1 dimethylbenzoanthracene (DMBA) to test the effects on, respectively, the hepatic EROD activity in S9 supernatant fraction, and the frequency of micronucleated erythrocytes three days after the i.p. treatments, and compared to an unexposed group, to test its potential as a sentinel for biomonitoring studies. The EROD activity was approximately two-fold higher in fish from the impacted stretches than in fish from the less disturbed stretches (p < 0.05). Micronuclei (MN) frequency was also significantly different (p < 0.01) in DMBA-treated fish. The induced EROD activity in the impacted site suggests that organochlorinated pollutants are reaching the biota of the Paraíba do Sul River, confirming the suitability of Geophagus brasiliensis as a useful sentinel species to detect changes caused by xenobiotics(AU)

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A new approach for visual fish survey in reservoirs using underwater drones (remotely operated vehicle- ROV) is presented. The ROV was applied to identify abiotic gradients and to compare fish assemblages on the steep slopes in a tropical reservoir. The tested hypothesis is that fish are concentrated in the littoral zone due to the better physicochemical and habitat conditions, compared to deep and hypoxic layers. Twelve species were recorded (seven native, five exotic), with all species occurring in the littoral zone, seven species in the transition, and four in the profundal zone. A greater fish abundance and richness was found in the littoral zone corroborating the main hypothesis. The littoral zone was dominated by exotic cichlids (Cichla spp., Coptodon rendalli), while native catfish (Loricariichthys castaneus, Pimelodella lateristriga) occupied deeper areas. The fish distribution seems to be driven by local factors, such as oxygen availability and habitat structure. The preference for the littoral zone by alien cichlids may have led to the extirpation/decrease of native characids and induced catfishes to occupy deep habitats. Underwater drones can be a valuable tool for the simultaneous collection of abiotic/biotic data, especially in deep reservoirs with complex habitats, resulting in advances in the environmental monitoring. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10750-021-04790-9.

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The reproductive strategy of the non-native predator cichlid Cichla kelberi was determined to explain its success after more than 60 years of being introduced into an isolated reservoir in southeastern Brazil. This was one of the first-known translocations of the genus Cichla out of its natural range. Macro- and microscopy characteristics of the gonadal development stages and the maturation phases, along with the reproductive features (size at first maturation size, gonado-somatic index and sex ratio), were described. It was hypothesized that the stable conditions of the reservoir, with low connectivity, weakly defined spatial gradient and slight seasonal changes in environmental variables, favour the equilibrium strategy that enables predators to have high offspring survivorship because of great parental investment in individual progeny. Sex ratio was well balanced, with males and females reaching first maturity between 30.0 and 28.6 cm total length (LT ), respectively. The stages of oocyte (primary and secondary growth, vitellogenic and atresia) and spermatocyte (spermatogonia, spermatocytes, spermatids and spermatozoa) development were identified. Five phases of gonadal development (immature, developing, spawning capable, regressing and regenerating) were described for both sexes. A long reproductive season was found, with spawning peaks in August/September and, to a lesser extent, in April/May. Parental care and spawns in parcels (batch spawns) corroborated the raised equilibrium strategy that was effective in this isolated reservoir. This species developed reproductive mechanisms that fit to different environmental conditions, with multiple spawning being associated with lentic environments and asynchronous development of oocytes, which are released over long periods. The reproductive plasticity in reservoirs may be one of the main factors inherent to the successful of colonization and establishment of the peacock bass in the environments in which they were introduced.

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Classifying species into groups based on taxonomic relationship and functions are objective approaches to evaluate environmental and anthropogenic influences on coastal fishes. We evaluated temporal (1993-1995 and 2012-2015) changes in the taxonomic and functional indices in three zones of a tropical bay heavily impacted over the recent decades. We tested the hypothesis that both indices decrease over time as result of the environmental degradation. A decrease in the taxonomic richness and abundance was observed mainly of the inner zone. The functional structure remained relatively stable, but the functional originality decreased significantly between the two periods. This functional loss is of particular concern because the loss of species with unique treats may generate a series of ecosystem damage. This information tells us that the use of functional indices is essential to complement taxonomic assessments and to detect a more detailed understanding of the real dimension of biodiversity loss in impacted environments.

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The spatial structure of the fish diversity and site-scale and landscape-scale environmental effects were investigated across hierarchical levels in tropical coastal ecosystems. Total diversity (γ) was hierarchically partitioned into α and ß components using both the additive and multiplicative methods. A model selection based on the AICc was applied to generalized linear mixed models relating diversity measures to environmental variables and including random effects for hierarchical levels and season. Short-term seasonal effects were negligible. Spatial effects were more relevant at the site level and negligible at the subregion level, due to the high spatial heterogeneity and the natural pooling of ecosystems, respectively. Site-scale environmental effects were more relevant at the subregion level, with eutrophic conditions (continental influence) favoring the species richness (α and γ) and higher absence of species (ßA) in oligotrophic conditions (marine influence). At the system level, the positive effect of the distance from the ocean on γ and higher ßA in oligotrophic conditions reinforced the positive continental influence on fish diversity. Environmental homogenization processes were most likely associated with the negative effect of the pasture cover on α at the system level, and γ and ßA at the site level. The negative effect of the forest cover on the later diversity measure evidenced its relevance to maintain richer but more similar assemblages, whereas the positive continental influence was most likely due to the loss of stenohaline marine species. This study evidenced that disentangling spatial, land use, and marine vs. continental effects on diversity components is critical to understand the primary determinants of the fish diversity in tropical coastal ecosystems.

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The Paraíba do Sul River (PSR) drainage basin in Southeastern Brazil covers one of the most industrialized and densely populated regions of the country. The impact of chemical contamination on the PSR basin seems to be more pronounced in its middle reach where a number of potentially polluting plants are located. In this study, we used hepatic EROD activity - a biomarker of exposure to CYP1A-inducing pollutants (e.g. PAHs, PCDD/Fs, PCBs) - and the incidence of micronucleated erythrocytes (Mn) in the peripheral blood - a biomarker of effects of DNA-damaging agents (e.g. PAHs) - to evaluate the effects of pollution on two native fish species, Geophagus brasiliensis and Pimelodus maculatus. Results showed that the incidence of Mn and EROD in G. brasiliensis and P. maculatus from the two most downstream sites (Três Rios Town and Piabanha River) were markedly higher than the incidence of Mn and EROD recorded in fish from the most upstream site (Funil Reservoir). Our findings are consistent with the view that CYP1A-inducing activity and increased DNA-damage are found in fish caught in sampling sites located downstream of the stretch where there are several industries that are potential sources of PAHs and CYP1A-inducing contaminants.(AU)

O rio Paraíba do Sul (RPS) drena uma das mais industrializadas e densamente povoadas áreas do sudeste do Brasil. O impacto de contaminação química no RPS parece ser mais pronunciado no segmento médio da bacia onde se localiza grande número de indústrias potencialmente poluidoras. Neste estudo, foi avaliada a atividade hepática EROD um biomarcador de exposição a poluente indutores da CYP1A (e.g. HAPs, PCDD/Fs, PCBs) e a incidência de eritrócitos micronucleados (Mn) no sangue periférico um biomarcador de efeitos de agentes de danificação do DNA- (e.g. HAPs) para avaliar o efeito de poluição sobre dois peixes nativos, Geophagus brasiliensis e Pimelodus maculatus. Os resultados apresentaram que a incidência de Mn e EROD em G. brasiliensis e P. maculatus nos dois locais no trecho mais baixo (Três Rios e rio Piabanha) foi marcadamente mais elevada do que a incidência e a atividade EROD registradas em peixes dos locais mais à montante (reservatório do Funil). Estes resultados são consistentes com a visão de que atividade indutora de CYP1A e elevadora de danos no DNA são encontradas em peixes capturados em locais abaixo do trecho onde grande número de indústrias são potenciais fontes de poluição de indutores de contaminantes HAPs e CYP1A.(AU)

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