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The Araguaia River is an important watercourse located in Central Brazil and well known for its diversity of fish fauna. Differences between landscape and resources in the distinct environments existing in a floodplain can determine the success of a species. This study presents a list of ichthyofauna species found in lentic and lotic environments in the floodplain of the Araguaia River basin, bordering Mato Grosso and Goiás States. We carried out sampling in July 2019, during the dry season, using diverse fish collection strategies, such as waiting nets, trawl, cast net and fishing rods. Were distributed 12 sampling points between lentic and lotic environments and we captured a total of 168 individuals of 42 species, 19 families and six orders. The predominant orders were Characiformes, Siluriformes and Cichliformes, while the families were Serrasalmidae, Characidae, Triportheidae, Curimatidae and Anostomidae. The genera Triportheus, Psectrogaster and Moenkhausia were the most abundant, while Pimelodus was the most dispersed. Results showed greater abundance and diversity in the lentic environment than in the lotic one, with top-of-the-chain species in both. The variance between environments and the presence of species that are endemic, recently described, of undefined taxonomic status, and bioindicators, highlight the importance of conserving and further studying the ichthyofauna in the Araguaia River basin.

Clariidae, commonly referred as air-breathing or walking catfishes, are a family of catfish distributed in Africa, Asia Minor, the Indian subcontinent, and Southeast Asia. Some species are highly valuable as food fish. As part of ongoing ichthyofaunal surveys in the Central Mahakam River, East Kalimantan, Indonesia, we present our findings from Clarias specimens collected from Central Mahakam River. We document C. pseudonieuhofii Sudarto, Teugels & Pouyaud, 2004, in the Central Mahakam River, Kutai Kartanegara Regency, East Kalimantan, which is located approximately 1200 km from the type locality in West Kalimantan.

Three specimens of Spottobrotula mahodadi Cohen & Nielsen, 1978, collected from Perak, Malaysia in July 2023, represent the first record of the species from the Straits of Malacca. Previous records had been limited to the Andaman Islands and Ranong, Thailand in the Andaman Sea. The newly collected specimens are described in detail, with morphometric and meristic data provided.

Aim The present study investigated the social impacts caused by the construction of a large hydropower dam (Lajeado Dam) on artisanal fishers in the Middle Tocantins River, evaluating how the impoundment affected fishing techniques (locations, transport and gears), operation (income, effort and costs), and fisher’s well-being. Methods The study interviewed 30 artisanal fishers (Colony Z-04, Porto Nacional, TO) between August and October 2018 with the application of a structured questionnaire. Results Results indicated that fishing is socially important as a source of income and occupation, carried out essentially by men with low levels of formal education. Fishers reported, however, significant changes in the fishery system after the impoundment of the Tocantins River. The main fishing area was maintained, but fishers abandoned some sites. There were significant changes in fishing equipment, with an increase in the use of aluminum boats and outboard engines, and a reduction in the use of various gears, replaced by the use of gillnets. Almost all fishers (96.6%) declared that fishing effort and the financial costs increased after damming. Many also reported an increase in financial income (70%), but part reported a decrease, no change or could not say. The majority reported that the impoundment damaged the fishing activity (80%) and their well-being (individual and their families; 83.3%); dissatisfaction with the profession also increased. Conclusions Results indicated that the impoundment created by Lajeado Dam impacted several aspects of artisanal fisheries in the Middle Tocantins, with a wide perception of damage, which indicates that working conditions of fishers have declined. This information is relevant and can support fisheries management in the Tocantins River Basin, in order to balance societal demands with sustainability goals and fisher’s needs. Resumo: Objetivo O presente estudo investigou os impactos sociais causados pela construção de uma grande barragem hidrelétrica (barragem de Lajeado) sobre os pescadores artesanais que atuam no Médio Rio Tocantins, avaliando como o represamento do rio afetou as técnicas de pesca (locais, transporte e petrechos), sua condução (geração de renda, esforço e custos) e o bem-estar dos pescadores. Métodos O estudo entrevistou 30 pescadores artesanais (Colônia Z-04, Porto Nacional, TO) entre agosto e outubro de 2018 com a aplicação de um questionário estruturado. Resultados Os resultados indicaram que a pesca tem grande relevância social como fonte de renda e geração de emprego, exercida essencialmente por homens com baixo nível de escolaridade. No entanto, os pescadores relataram mudanças significativas na atividade pesqueira após o represamento do rio Tocantins. A principal área de pesca foi mantida, mas os pescadores abandonaram alguns locais. Houve mudança notável nos equipamentos de pesca, com aumento significativo no uso de barco de alumínio e motor, redução no uso de diversos petrechos, e aumento no emprego de malhadeiras. Quase todos os pescadores (96%) declararam aumento no tempo gasto com a pesca e no custo financeiro envolvido. A maioria também afirmou aumento da renda financeira (70%), embora parte tenha relatado diminuição, ausência de alteração ou não soube dizer. A grande maioria relatou que o represamento prejudicou a atividade pesqueira (80%) e seu bem estar (individual e de sua família; 83.3%); também houve aumento na insatisfação com a profissão. Conclusões Os resultados indicaram que o represamento da usina de Lajeado impactou diversos componentes da pesca artesanal no Médio Tocantins, com ampla percepção de prejuízo, o que indica piora nas condições de trabalho dos pescadores. Essas informações são relevantes para o ordenamento e gestão pesqueira na bacia do Rio Tocantins, no intuito de equilibrar as demandas da sociedade com metas de sustentabilidade e necessidades dos pescadores.

To effectively conserve coral reef ecosystems, it is essential to monitor changes in fish fauna using minimally invasive methods. In this study, we conducted a fish survey in the Dongsha Atoll using eDNA metabarcoding. Analyzing 37 sequencing units from 26 water samples collected across 12 sites from May 2017 to September 2018, we identified 421 species from 79 families. Among these, 192 species had not been recorded in previous conventional surveys. Some of these newly recorded species are fast-swimmers, while others may be larvae or eggs, which are challenging to observe visually. However, 68% of species documented in previous records were not detected in our study. This limitation is likely due to insufficient samplings, primer specificity, fish characteristics, and rapid DNA degradation in the dynamic physical and chemical conditions (e.g., temperature, pH) of the coastal environment. Despite that eDNA metabarcoding cannot capture the full range of species within the atoll, it effectively complements visual census surveys by enriching our understanding of the diverse fish community in marine habitats.

The intrusion of non-native species into freshwater ecosystems can lead to rapid shifts in fish community dynamics, posing significant threats to biodiversity and ecological stability. In this study, we examined the changes in the fish community within the Kerkini Reservoir, a Ramsar Site in Greece, influenced by the establishment of invasive fish species. Through standardized seasonal surveys conducted in 2007–2008 and 2023, we assessed changes in fish species composition, abundance, and functional traits. Our findings revealed a shift in dominance, with invasive species such as Gymnocephalus cernua emerging as key players in the reservoir's fish fauna. Moreover, high numbers of fish specimens and biomass were recorded, highlighting the reservoir’s high productivity. However, concerns arise regarding the ecological impacts of invasive species, particularly G. cernua , which exhibits traits associated with ecological disruption and competition with native species. A shift towards the dominance of species with shorter lifespans, smaller sizes and lower trophic levels was observed. In addition, the observed decline in native species abundance, coupled with poor ecological quality assessments, underscores the need for proactive management measures to preserve ecosystem integrity. This study contributes valuable insights into the ecological dynamics of a system considered a biodiversity hotspot. It also highlights the proliferation of invasive fish species as a primary driver and underscores the importance of ongoing monitoring and conservation efforts. However, future research is needed, focusing on further understanding the long-term effects of invasive species establishment and their implications for native fish populations and ecosystem functioning.

Abstract The Golfão Maranhense is an extensive estuarine complex that provides nursery grounds and other habitats for several fish species, as well as a wealth of resources for the coastal and estuarine artisanal fisheries of the Maranhão state, in northern Brazil. The present study provides a comprehensive inventory of marine and estuarine teleost fishes of the Golfão Maranhense based on field samplings, analyses of voucher specimens from local collections and literature data. This inventory presents a total of 163 species of teleosts belonging to 107 genera, 57 families and 27 orders. The order Perciformes prevailed in terms of richness (27 species), followed by Acanthuriformes, Carangiformes, Clupeiformes and Siluriformes. The most diverse family was Sciaenidae (19 species), followed by Carangidae, Ariidae, Engraulidae and Gerreidae. Among the 163 species recorded, 18 are new occurrences for the Golfão Maranhense. According to the IUCN Red List, seven species are classified as Vulnerable. Considering the official Brazilian list of threatened species, five species appear as Vulnerable and one – Epinephelus itajara – as Critically Endangered. Four of the recorded species (Butis koilomatodon, Trypauchen vagina, Omobranchus sewalli and Oreochromis niloticus) are exotic, and were probably introduced into the study area by shipping, fish farms or by the extension of their range along the Brazilian coast. The present study organizes, updates and expands the known and relatively limited data on the fish fauna of the Golfão Maranhense, highlighting the need for further research towards gathering data for conservation and management of the ichthyofauna of this important estuarine complex in the Northern Brazilian Coast. Resumo O Golfão Maranhense é um extenso complexo estuarino caracterizado como uma fundamental área de berçário e habitat para diversas espécies de peixes, fornecendo grande riqueza de recursos naturais para a pesca artesanal estuarina e costeira do estado do Maranhão. O presente estudo constitui um inventário abrangente dos peixes teleósteos marinhos e estuarinos do Golfão Maranhense baseado em coletas de campo, análise de vouchers de espécimes de coleções locais e dados da literatura. Este inventário apresenta um total de 163 espécies de teleósteos pertencentes a 107 gêneros, 57 famílias e 27 ordens. A ordem Perciformes dominou em termos de riqueza (27 espécies), seguida por Acanthuriformes, Carangiformes, Clupeiformes e Siluriformes. A família mais diversificada foi Sciaenidae (19 espécies), seguida por Carangidae, Ariidae, Engraulidae e Gerreidae. Entre as 163 espécies registradas, 18 são novas ocorrências para o Golfão Maranhense. Sete espécies estão classificadas como Vulneráveis de acordo com a lista vermelha da IUCN. Considerando a lista brasileira oficial de espécies ameaçadas, cinco espécies têm status Vulnerável e uma – Epinephelus itajara – está Criticamente em Perigo. Do total de registros, quatro espécies (Butis koilomatodon, Trypauchen vagina, Omobranchus sewalli e Oreochromis niloticus) são exóticas e provavelmente foram introduzidas na área de estudo por água de lastro de navios cargueiros, pela piscicultura ou pela extensão de sua área de ocorrência ao longo da costa brasileira. O presente estudo organiza, atualiza e amplia os dados conhecidos e relativamente limitados sobre a ictiofauna do Golfão Maranhense, destacando a necessidade de mais pesquisas para conservação e gestão da ictiofauna deste importante complexo estuarino da costa norte brasileira.

The conservation challenges facing freshwater ecosystems necessitate broadening our science from understanding individual species loss to anticipating multi-faceted changes to biodiversity. In recent decades, the process of biotic homogenization by which regional biotas become more similar through time has attracted considerable attention. Here, we (1) quantified spatial and temporal changes in taxonomic and functional similarity of fish assemblages among Neotropical reservoirs, (2) determined nonnative species contributions to changes in taxonomic and functional composition, and (3) evaluated relationships between the changes in taxonomic and functional similarity among reservoirs. We did so by considering different spatial scales: inter- and intra-ecoregions. At inter-ecoregion scale, reservoir fish assemblages have become taxonomically homogenized over time, whereas functional trait composition has tended to differentiate. At intra-ecoregion scale, we detected both taxonomic and functional differentiation over time. Despite these overall trends, different ecoregions exhibited considerable variation in patterns of fish faunal homogenization and differentiation. We found a moderate positive relationship between changes in mean taxonomic and functional similarity among reservoirs at inter-ecoregion scale, which was no longer evident within ecoregions. In conclusion, this study demonstrates the strong scale-dependence of perceived patterns in homogenization, and further highlights the magnitude of threats to freshwater biodiversity in the Neotropical ecosystems.

This study assessed the impacts of climatic parameters (rainfall and temperature) and environmental variables (transparency, depth, chloride, TS, TSS, TOC) on the abundance of commercially important fish species in Esa-Odo. The research question was to find out if climatic and environmental factors influence the abundance of fish species in an afro-tropical reservoir. Fish species were collected on a monthly basis for two annual cycles covering both dry and rainy seasons. GIS-based climatic data was used to determine the relationship between climatic conditions and fish species abundance. Results showed that the highest abundance of fish was recorded during the rainy season, with Oreochromis niloticus being the most dominant species throughout the sampling period. Trend analysis revealed that variations in climate and environmental parameters influenced the abundance of different fish species in the reservoir. Mann-Kendal analysis indicated that an increase in rainfall led to an increase in reservoir depth, a decrease in transparency levels, and a reduction in temperature, with a Sen’s slope value of -38. Additionally, CCA and correlation matrix results demonstrated that climate and environmental parameters significantly influenced fish species abundance. The study emphasized the importance of climatic and environmental factors in the abundance of fish species in the reservoir, providing valuable information for future research on fishery resources. Governments and stakeholders were urged to prioritize the conservation and management of the reservoir’s fish population to prevent declines.

The lack of knowledge about freshwater biodiversity in remote areas like montane Andean rivers is noticeable and hinder the development of efficient conservation plans for aquatic ecosystems. Habitat requirements of tropical Andean fishes have been poorly analysed, despite the relevance of these ecological features on the fish conservation strategies. The present study aimed to examine fish assemblages along the altitudinal gradient in tropical Andean rivers and their relationship to habitat features to detect the most relevant abiotic factors and their implication on conservation. This study was conducted on a regional scale, along six basins located in tropical Andes (500 to 2,692 m a.s.l.). We studied fish diversity and distribution and their habitats along these elevation gradients. We found 6,320 specimens from 53 genera. Our analysis for the six most common and widely distributed genera (Astroblepus, Brycon, Bryconamericus, Chaetostoma, Pimelodella and Trichomycterus) underlines the relevance of hydromorphological variables on fish community structure in the Andean montane rivers, whereas human alterations seem to be less significant. These findings could be useful for current management and conservation strategies considering present threats over tropical montane rivers.