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Global warming has significantly altered fish distribution patterns in the ocean, shifting towards higher latitudes and deeper waters. This is particularly relevant in high-latitude marine ecosystems, where climate-driven environmental changes are occurring at higher rates than the global average. Species Distribution Models (SDMs) are increasingly being used for predicting distributional shifts in habitat suitability for marine species as a response to climate change. Here, we used SDMs to project habitat suitability changes for a range of high-latitude, pelagic and benthopelagic commercial fish species and crustaceans (10 species); from 1850 to two future climate change scenarios (SSP1-2.6: low climate forcing; and SSP5-8.5: high climate forcing). The study includes 11 Large Marine Ecosystems (LME) spanning South America, Southern Africa, Australia, and New Zealand. We identified declining and southward-shifting patterns in suitable habitat areas for most species, particularly under the SSP5-8.5 scenario and for some species such as Argentine hake (Merluccius hubbsi) in South America, or snoek (Thyrsites atun) off Southern Africa. Geographical constraints will likely result in species from Southern Africa, Australia, and New Zealand facing the most pronounced habitat losses due to rising sea surface temperatures (SST). In contrast, South American species might encounter greater opportunities for migrating southward. Additionally, the SSP5-8.5 scenario predicts that South America will be more environmentally stable compared to other regions. Overall, our findings suggest that the Patagonian shelf could serve as a climate refuge, due to higher environmental stability highlighting the importance of proactive management strategies in this area for species conservation. This study significantly contributes to fisheries and conservation management, providing valuable insights for future protection efforts in the Southern Hemisphere.

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Coastal and estuarine systems play an important role in the maintenance of marine biodiversity, providing nursery, feeding, developmental and reproductive areas for terrestrial and aquatic species. The Fundão dam collapse is considered one of the biggest environmental disasters in Brazil, causing great social, economic and ecological damage in the affected areas. In our study, we used beta diversity and its components as a tool to monitor the spatio-temporal variation of fish larvae in four marine areas adjacent to the Doce River. The results show that the four areas undergo different spatio-temporal dynamics, with the composition of fish larvae in the Doce being simplified in the last years after the dam burst, compared to the other adjacent marine areas. In addition, turbidity is an important factor that has caused the homogenization of the larval composition of the Doce, demonstrating that mud resuspension events can cause a decrease in diversity and also suggesting the toxicity of the mud composition. The change from negative to positive additive and colonizing components in recent years suggests a slight recovery of diversity in the Doce compared to other marine areas. Finally, we have shown that some species may be tolerant to the impact, but with probable behavioral, energetic and physiological costs, which justifies the constant monitoring of these areas.

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ABSTRACT In Colombia, ichthyozoonoses caused by helminths are little studied and remain neglected by the public health sector, representing an interaction to be explored regarding biodiversity and health. Caquetia kraussii is a native fish of Colombia and Venezuela that is economically important due to its high consumption by local communities. This research records the fauna of parasitic helminths associated with C. kraussii in a coastal lagoon system in the Colombian Caribbean. Thirty-two specimens of C. kraussii were captured and inspected in February and December 2020, resulting in the collection of 242 helminths at the metacercariae stage and adults. Parasites included metacercaria of the trematodes Clinostomum sp., Austrodiplostomum sp., two forms of Posthodiplostomum and adults of Oligogonotylus andinus, and adults of the acanthocephalan Neoechinorhynchus sp. These results indicate that C. kraussii acts as a definitive host for O. andinus and Neoechinorhynchus sp., and as an intermediate host for Clinostomum sp., Posthodiplostomum spp. and Austrodiplostomum sp. This research reports for the second time a population of O. andinus in Colombia and the occurrence of a morphoespecies of the genus Neoechinorhynchus that could constitute a new record for Colombia. In addition to contributing to the knowledge of the diversity of fish-associated helminths, the results of this research will make it possible to generate recommendations for the management and control of helminthiasis in artificial fish farming systems that are supplied by natural tributaries, and favor the establishment of hosts and parasites.

RESUMEN En Colombia, las ictiozoonosis causadas por helmintos son poco estudiadas y permanecen desatendidas desde el sector de la salud pública, representando una interacción por explorar en términos de biodiversidad y salud. Caquetia kraussii es un pez nativo de Colombia y Venezuela de importancia económica, debido a su alto consumo por parte de comunidades locales. Esta investigación registra la fauna de helmintos parásitos asociados a C. kraussii en un sistema de laguna costera en el Caribe colombiano. En febrero y diciembre de 2020 se examinaron 32 especímenes de C. kraussii, de los que se recolectaron 242 helmintos en los estadíos de metacercaria y adulto. Los parásitos incluyeron metacercarias de los tremátodos Clinostomum sp., Austrodiplostomum sp., dos morfoespecies de Posthodiplostomum spp. y adultos de Oigogonotylus andinus además de adultos del acantocéfalo (Eoacanthocephala) Neoechinorhynchus sp. Estos resultados indican que C. kraussii actúa como hospedador definitivo de O. andinus. y Neoechinorhynchus sp., y como hospedador intermediario de Clinostomum sp., Posthodiplostomum spp. y Austrodiplostomum sp. Se reporta por segunda vez una población de O. andinus en Colombia y la ocurrencia de una morfoespecie del género Neoechinorhynchus que podría ser un reporte nuevo para Colombia. Además del aporte al conocimiento de la diversidad de helmintos asociados a peces, los resultados de esta investigación podrían ser aprovechados para generar recomendaciones para el manejo y control de helmintiasis en sistemas piscícolas artificiales que se surten de afluentes naturales y favorecen el establecimiento de hospederos y parásitos.

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A new species of Eigenmannia is described from the Rio Branco basin, Roraima, Brazil, based on morphological and molecular datasets. It is distinguished from all congeners by the following combination of characters: lateral line stripe extending from first perforated lateral line scale to distal portion of caudal filament, presence of superior midlateral stripe with origin posterior to end of body cavity anal-fin hyaline, caudal filament corresponding to 15.2%-43.1% LEA, subterminal mouth, ii,14-16 pectoral-fin rays, 166-219 anal-fin rays, 10-13 scale rows above lateral line at vertical through posterior tip of pectoral fin, 100-128 scales on lateral line, 22-28 premaxillary teeth, 19-23 dentary teeth, 7-10 endopterygoid teeth, depth of posterodorsal expansion on infraorbitals 1 + 2 half as long as infraorbitals 1 + 2 length, basibranchial 1 unossified, 13 precaudal vertebrae, and length of coronomeckelian bone corresponding to 20% of Meckel's cartilage length. The new species has significant genetic divergence from species with accessible DNA sequences in public repositories, ranging from 10.8% to 17.7%. An osteological description of the new species, a review of Eigenmannia cytochrome c oxidase subunit I (COI) sequences available in public repositories based on voucher examination, and a hypothesis of phylogenetic relationships for the new species based on COI are provided. The critical importance of including voucher examination as one of the steps in the pipeline for using DNA sequences present in public repositories in taxonomic and phylogenetic studies is discussed.

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The Vaupés River stands out as one of the few within the Amazon basin due to its numerous rapids. These riverine fast-flowing sections not only provide habitat to highly specialized fishes but also function as natural barriers hindering the movement of fish along its course. During a fish-collecting expedition in the lower Vaupés River basin in Colombia, 95 species were registered belonging to 30 families and seven orders. Despite recent inventories in the region, our comprehensive sampling efforts particularly focused on the rapids and associated rheophilic fauna, allowing us to contribute the first records of four fish species in Colombia (Mylopluslucienae Andrade, Ota, Bastos & Jégu, 2016, Tometesmakue Jégu, Santos & Jégu, 2002, also first record of the genus, Leptodoraspraelongus (Myers & Weitzman, 1956), and Eigenmanniamatintapereira Peixoto, Dutra & Wosiacki, 2015) and six presumably undescribed species (i.e., Jupiaba sp., Moenkhausia sp., Phenacogaster sp., Bunocephalus sp., Hemiancistrus sp., and Archolaemus sp.). In this study, a commented list of the ichthyofauna of these environments is presented, as well as a photographic catalog of fish species integrated into the CaVFish Project - Colombia.

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We review the negative impacts of vinasse, a byproduct of alcohol distillation, on Brazil's freshwater ecosystems. We found a total of 37 pollution events between the years 1935 and 2023, with this number almost certainly an underestimate due to underreporting and/or unassessed events. Pollution by vinasse occurred both through accidents (e.g., tank failure) and deliberately (i.e., opening of floodgates), although in many cases the causes remain undetermined. All pollution events caused fish kills, with some records reporting negative effects on other organisms as well (i.e., crustaceans and reptiles). Pollution by vinasse, and associated negative effects, was reported for 11 states, with a notable number of cases in São Paulo. Most cases of vinasse pollution and negative impacts on biodiversity were recorded in rivers, followed by streams and reservoirs. Some of the affected river systems harbour threatened freshwater fishes. Hydrological connectivity means that pollution could have propagated along watercourses. Given these consequences of vinasse pollution on biodiversity, ecosystem functioning and services, we recommend a number of remedial actions.

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Species of the catfish genus Rineloricaria are common in the Paraíba do Sul River basin, in southeastern Brazil; here we present a revision of the taxonomic diversity and geographic distribution of the species of the genus inhabiting the basin, based on novel morphologic and molecular data. Five species delimitation methods based on cytochrome C oxidase subunit 1 nucleotide sequences yielded comparable molecular operational taxonomic units. The automatic barcode gap discovery, assemble species by automatic partitioning, barcode index number, and Bayesian implementation of the Poisson tree process methods supported the recognition of five evolutionary lineages. These taxonomic units were assigned to the previously described Rineloricaria nigricauda, Rineloricaria steindachneri, Rineloricaria zawadzkii, and Rineloricaria nudipectoris, and an additional undescribed species. R. zawadzkii was further divided into two intraspecific geographically structured lineages using the generalized mixed Yule coalescent delimitation method. A maximum likelihood phylogenetic analysis revealed that the five lineages from the Paraíba do Sul have closer relationships to different species from southern and southeastern Brazil (Ribeira de Iguape, Lagoa dos Patos, Uruguay, Paraguay, and Parana river basins) than to each other. Based on the analysis of lectotypes, recently collected material, and specimens from ichthyological collections, the poorly described R. nigricauda and R. steindachneri are redescribed following current descriptive standards. The undescribed species from the middle and upper Paraíba do Sul River basin is formally described. The description of a new species, along with the description of species boundaries in R. nigricauda and R. steindachneri, contributes to the knowledge of the ichthyofauna of the Paraíba do Sul River basin and adjacent coastal drainages of southeastern Brazil. An identification key for the species of Rineloricaria occurring in the Paraíba do Sul River basin is provided.

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This study aimed to identify and characterize isolates of Francisella salimarina associated with an outbreak on a marine fish farm in Brazil and to analyse their genetic variability and antimicrobial susceptibility. In 2021, diseased cobias (Rachycentron canadum, n = 10) and dusky groupers (Epinephelus marginatus, n = 10) were sampled and subjected to bacteriological and pathological examinations. The isolates obtained were morphologically and biochemically characterized and identified by matrix-assisted laser desorption/ionization-time of flight (MALDI-ToF) and 16S rRNA gene sequencing. The genetic diversity of these isolates was analysed using repetitive extragenic palindromic-polymerase chain reaction (REP-PCR). Antimicrobial susceptibility was assessed using the disk diffusion technique. Macroscopically, the fish presented skin ulcerations, ocular lesions, hepatomegaly and splenomegaly. A pleomorphic, gram-negative, catalase- and oxidase-positive bacterium was isolated from seven cobias and two groupers. The 16S rRNA gene sequences showed >99% coverage and identity with other deposited sequences of F. salimarina. The results of the biochemical analysis corresponded to these bacterial species. Histologically, granulomas were observed in the spleen, liver and heart of the cobias (n = 6), and necrotizing and fibrinous dermatitis and myositis were identified in some groupers (n = 2). The isolates exhibited the same banding pattern when REP-PCR was performed, indicating that they were clonally related. Finally, the antibiogram test, no inhibition halo was observed for amoxicillin and trimethoprim-sulfamethoxazole. To our knowledge, this is the first report of F. salimarina infection in cobias and dusky groupers.

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Intending to compare in vitro cell growth in different conditions, we established cell cultures using fin biopsies of two freshwater fishes, Astyanax bimaculatus and Geophagus proximus. Three different culture media (Leibovitz-L-15, Dulbecco's Modified Eagle Medium [DMEM], and 199) were employed, with or without the addition of AmnioMax, maintaining a standard temperature of 29°C. Based on the results obtained, we standardized a cell growth protocol in which medium 199 was less efficient for both species. Notably, G. proximus cells exhibited superior proliferation in DMEM and L-15 media, whereas A. bimaculatus cells demonstrated better parameters exclusively in the DMEM medium. Successful subculturing of cells with good proliferation index was observed, accompanied by preserved morphological characteristics. Therefore, the methodology outlined in this study represents an advancement in establishing fish cell cultures.

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In the present study, we examined 30 individuals of introduced African cichlids, Oreochromis niloticus and Coptodon rendalli, collected in a river spring of the Pardo River, Paranapanema River basin, southeastern Brazil. Based on morphological and molecular analyses of the partial LSU rDNA gene, we identified four species of monogeneans, Cichlidogyrus tilapiae, C. thurstonae, C. mbirizei, and Scutogyrus longicornis on the gills of O. niloticus, whereas individuals of C. rendalli were infested only with C. papernastrema. This is the first record of C. mbirizei and C. papernastrema in tilapias from Brazil. The ecological consequences of the introduction of exotic species of tilapia such as O. niloticus and C. rendalli along with their monogenean parasites in a wild environment represented by a river spring are discussed. Our new molecular data on Cichlidogyrus and Scutogyrus contribute to the investigation of the phylogenetic interrelationships of these widely distributed genera of monogeneans since their species composition is still unsettled.

Title: Parasites (Monogenea) des tilapias Oreochromis niloticus et Coptodon rendalli (Cichlidae) dans une source au Brésil. Abstract: Dans la présente étude, nous avons examiné 30 individus de cichlidés africains introduits, Oreochromis niloticus et Coptodon rendalli, collectés dans une source fluviale du fleuve Pardo, bassin du fleuve Paranapanema, dans le sud-est du Brésil. Sur la base d'analyses morphologiques et moléculaires du gène partiel de l'ADNr LSU, nous avons identifié quatre espèces de monogènes, Cichlidogyrus tilapiae, C. thurstonae, C. mbirizei et Scutogyrus longicornis sur les branchies d'O. niloticus, alors que les individus de C. rendalli étaient infestés uniquement par C. papernastrema. Il s'agit du premier signalement de C. mbirizei et C. papernastrema chez des tilapias du Brésil. Les conséquences écologiques de l'introduction d'espèces exotiques de tilapia telles que O. niloticus et C. rendalli ainsi que leurs monogènes parasites dans un environnement sauvage représenté par une source fluviale sont discutées. Nos nouvelles données moléculaires sur Cichlidogyrus et Scutogyrus contribuent à l'étude des interrelations phylogénétiques de ces genres de monogènes largement distribués puisque leur composition spécifique est encore incertaine.

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Antimicrobial-resistant bacteria (ARB) from the intestinal contents of wild fish may have a relevant ecological significance and could be used as indicators of antimicrobial-resistance dissemination in natural bacterial populations in water bodies impacted by urban contamination. Thus, the occurrence of ARB in the intestinal contents of pelagic and demersal wild fishes captured in anthropogenic-impacted Coquimbo Bay in Chile was studied. Culturable counts of total and antimicrobial-resistant bacteria were determined by a spread plate method using Trypticase soy agar and R2A media, both alone and supplemented with the antimicrobials amoxicillin, streptomycin, florfenicol, oxytetracycline and ciprofloxacin, respectively. Heterotrophic plate counts of pelagic and demersal fishes ranged from 1.72 × 106 CFU g-1 to 3.62 × 109 CFU g-1, showing variable proportions of antimicrobial resistance. Representative antimicrobial-resistant isolates were identified by 16S rRNA gene sequencing, and isolates (74) from pelagic fishes mainly belonged to Pseudomonas (50.0%) and Shewanella (17.6%) genera, whereas isolates (68) from demersal fishes mainly belonged to Vibrio (33.8%) and Pseudomonas (26.5%) genera. Antimicrobial-resistant isolates were tested for susceptibility to 12 antimicrobials by an agar disk diffusion method, showing highest resistance to streptomycin (85.2%) and amoxicillin (64.8%), and lowest resistance to oxytetracycline (23.2%) and ciprofloxacin (0.7%). Only furazolidone and trimethoprim/sulfamethoxazole were statistically different (p < 0.05) in comparisons between isolates from pelagic and demersal wild fishes. Furthermore, an important number of these isolates carried plasmids (53.5%) and produced Extended-Spectrum-ß-lactamases (ESBL) (16.9%), whereas the detection of Metallo-ß-Lactamases and class 1-integron was rare. This study provides evidence that wild fish are important reservoirs and spreading-vehicles of ARB, carrying plasmids and producing ESBLs in Chilean marine environments.

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A new labrid fish species, Halichoeres sanchezi n. sp., is described from eight specimens collected in the Revillagigedo Archipelago in the tropical eastern Pacific Ocean, off the coast of Mexico. The new species belongs to the Halichoeres melanotis species complex that is found throughout the region, differing by 2.4% in the mtDNA cytochrome c oxidase I sequence from its nearest relative, H. melanotis from Panama, and 2.9% from Halichoeres salmofasciatus from Cocos Island, off Costa Rica. The complex is distinguished from others in the region by having a black spot on the opercular flap and a prominent black area on the caudal fin of males. The juveniles and initial phase of the new species closely resemble those of H. salmofasciatus and Halichoeres malpelo from Malpelo Island of Colombia, differing in having an oblong black spot with a yellow dorsal margin on the mid-dorsal fin of initial-phase adults as well as on juveniles. In contrast, the terminal-phase male color pattern is distinct from other relatives, being vermilion to orangish brown with dark scale outlines, a white patch on the upper abdomen, and a prominent black band covering the posterior caudal peduncle and base of the caudal fin. The new species adds to the list of endemic fish species for the isolated archipelago and is an interesting case of island endemism in the region. The discovery was made during the joint 2022 collecting expedition to the archipelago, which featured a pioneering collaborative approach to an inventory of an island ichthyofauna, specifically including expert underwater photographers systematically documenting specimens in situ, before hand-collection, and then photographed fresh, tissue-sampled, and subsequently vouchered in museum collections.

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There is no information on the species associated with the mesophotic reefs of Banderas Bay, located in the central Mexican Pacific. This study analysed the reef fish assemblage from three depths (50, 60 and 70 m) in three sampling sites of the southern submarine canyon of the Bay: Los Arcos, Bajo de Emirio and Majahuitas. Several analyses were performed to test the hypothesis that there are important differences in fish abundance and species composition between sites and depths. Twenty-two species of bony fishes grouped in 14 families were recorded. PERMANOVA results showed that there were no significant differences in fish diversity parameters between sites, indicating a certain uniformity in their distribution. However, nine species were exclusive to one site and depth (five singleton species with only one individual recorded and four unique species recorded only once). On the other hand, there were significant differences between depths, mainly between 50 and 70 m. Diversity decreases with depth and species composition changes. SIMPER, Shade Plot and NMDS analysis show the most representative species at each depth, with at least half of the species (11) recorded only at 50 m and four species at the deeper levels (60 - 70 m). The observed assemblage includes several of the most caught species in the shallow water artisanal fishery, which is the most traditional and common type of fishery in the Bay. In addition, the Pomacanthuszonipectus (Cortés angelfish) is of particular interest, as it has a special protection status in the official Mexican standard (NOM-059-SEMARNAT, 2010) due to its use as an ornamental species in aquaria. We hypothesised that the mesophotic zone may serve as a refuge for these fishes, so we propose that the information obtained is an important basis for new research aimed at the sustainable management of fisheries in the area.

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Annual fish have become attractive study models for a wide range of disciplines, including neurobiology. These fish have developed different survival strategies. As a result, their nervous system is under considerable selective pressure when facing extreme environmental situations. Fish from the Austrolebias group exhibit rapid neurogenesis in different brain regions, possibly as a result of the demanding conditions of a changing habitat. Knowledge of cerebral histology is essential for detecting ontogenic, anatomical, or cytoarchitectonic changes in the brain during the short lifespan of these fish, such as those reflecting functional adaptive plasticity in different systems, including sensory structures. The generation of an atlas of Garcialebias charrua (previously known as Austrolebias charrua) establishes its anatomical basis as a representative of a large group of fish that share similarities in their way of life. In this work, we present a detailed study of both gross anatomy and microscopic anatomy obtained through serial sections stained with the Nissl technique in three orientations: transverse, horizontal, and parasagittal planes. This atlas includes accurate drawings of the entire adult brain of the male fish Garcialebias charrua, showing dorsal, ventral, and lateral views, including where emergence and origin of cranial nerves. This brain atlas allows us to understand histoarchitecture as well as the location of neural structures that change during adult neurogenesis, enabling comparisons within the genus. Simultaneously, this atlas constitutes a valuable tool for comparing the brains of other fish species with different behaviors and neuroecologies.

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Temperate mesophotic reef ecosystems (TMREs) are among the least known marine habitats. Information on their diversity and ecology is geographically and temporally scarce, especially in highly productive large upwelling ecosystems. Lack of information remains an obstacle to understanding the importance of TMREs as habitats, biodiversity reservoirs and their connections with better-studied shallow reefs. Here, we use environmental DNA (eDNA) from water samples to characterize the community composition of TMREs on the central Chilean coast, generating the first baseline for monitoring the biodiversity of these habitats. We analyzed samples from two depths (30 and 60 m) over four seasons (spring, summer, autumn, and winter) and at two locations approximately 16 km apart. We used a panel of three metabarcodes, two that target all eukaryotes (18S rRNA and mitochondrial COI) and one specifically targeting fishes (16S rRNA). All panels combined encompassed eDNA assigned to 42 phyla, 90 classes, 237 orders, and 402 families. The highest family richness was found for the phyla Arthropoda, Bacillariophyta, and Chordata. Overall, family richness was similar between depths but decreased during summer, a pattern consistent at both locations. Our results indicate that the structure (composition) of the mesophotic communities varied predominantly with seasons. We analyzed further the better-resolved fish assemblage and compared eDNA with other visual methods at the same locations and depths. We recovered eDNA from 19 genera of fish, six of these have also been observed on towed underwater videos, while 13 were unique to eDNA. We discuss the potential drivers of seasonal differences in community composition and richness. Our results suggest that eDNA can provide valuable insights for monitoring TMRE communities but highlight the necessity of completing reference DNA databases available for this region.

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Body morphology is a valuable feature for distinguishing teleostean fishes. However, the utility of character variation in separate body regions has yet to be tested. The taxonomy of the Gerreidae family is controversial due to character overlapping among its fish species. This work aims to analyze and compare the body shape variation in three regions, cephalic, trunk, and caudal peduncle, using landmark data and geometric morphometric methods in 17 species and five genera of the family Gerreidae. The pattern of shape variation for the cephalic region consisted of well-defined character states exclusive of each species analyzed. Shape variation in the trunk and caudal peduncle regions does not distinguish all species in this study. This study showed that the dorsal cephalic profile is highly variable among the species, therefore, shape variation in this region is useful for distinguishing Gerreidae species. In contrast, some species within the same genus share similar shape states in the trunk and caudal peduncle regions, with the most shape variation in the dorsal profile and anal fin for the trunk and in the middle of the caudal peduncle.

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A taxonomic revision of Sturisoma is presented. Individuals including both type and non-type specimens of all valid species were examined. Sturisoma was found to comprise 10 valid species: Sturisoma barbatum, Sturisoma brevirostre, Sturisoma graffini, Sturisoma guentheri, Sturisoma lyra, Sturisoma monopelte, Sturisoma nigrirostrum, Sturisoma reisi, Sturisoma rostratum, and Sturisoma tenuirostre. Furthermore, four new species are described: Sturisoma ghazziae, new species, from the Araguaia River, belonging to the Tocantins-Araguaia basin, Central Brazil; Sturisoma careirensia, new species, from the middle Amazon basin, Brazil; Sturisoma rapppydanielae, new species, from the Purus River, Amazon basin, Brazil; and Sturisoma defranciscoi, new species, from the Putumayo and Solimões rivers, upper Amazon basin, Colombia, and Brazil. Sturisoma robustum is confirmed as synonym of S. barbatum, species registered along the Paraguay/Parana/La Plata River basin in Argentina, Brazil, and Paraguay. New records were found for S. nigrirostrum as present in the upper Amazon basin, in the Yavari River, Brazil, in addition to its already known locality, the Ucayali River, Peru. The distribution of the type species of the genus S. rostratum is limited to the lower portion of the Amazon basin in the Araguaia, Maranhão, Mearim, Tapajós, and Tocantins rivers and its affluents, Brazil, in contrast to the assumed widespread distribution across the main basins of South America, as previously proposed for the species; the Mearim River is a new record for the species. Updated diagnoses and descriptions are offered for species of Sturisoma, in addition to distribution maps and an identification key for the species.

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A large adult (138 mm head length) of the grenadier genus Coryphaenoides is described. It is identified as C. affinis hitherto known only from two juvenile type specimens collected by HMS Challenger off Uruguay in 1876. The diagnosis of the species is revised to include the discovery of considerable ontogenetic changes in squamation. Spinulation on the body scales are reduced or lost with size, while the armament of the head scales become amplified. The larger of the syntype specimens is designated as the lectotype. All three known specimens of C. affinis were collected in the southwestern Atlantic at depths between 3500 and 4000 m. A key for identification for the species of the subgenus Nematonurus is provided.

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Abstract The Río San Pedro and Río La Pasión lie within the Usumacinta River Basin, a globally significant center of freshwater fish diversity. Both rivers are listed among Central America's top 50 regions for conserving freshwater biodiversity. This study presents an updated checklist of 70 fish species, of which six are non-native to the Usumacinta River Basin. From these species, 69 are reported from the Río La Pasión and 56 reported from the Río San Pedro, representing higher species richness than previously reported. The checklist derives from a systematic survey of fishes conducted in 2019 and records available in public databases and published literature. Seventy-eight percent of the species were reported in both rivers, and Cichlidae and Poeciliidae had the most species. Secondary species represent 59% of the species reported, followed by peripheral species with 22% of the species. The species with highest fidelity in Río La Pasión were the armored catfish Pterygopichthys spp. and the livebearer Gambusia sexradiata; and the cichlids Thorichthys meeki and Oscura heterospila had highest fidelity in the Río San Pedro. Thorichthys helleri was widely distributed in both rivers. According to the IUCN Red List of Threatened Species, there are four species classified as Vulnerable in Río La Pasión. However, 62% of the species are of Least Concern, 25% of the species are Data Deficient, and 6% are listed as Not Evaluated. More research is needed to document the status of the fish fauna, and improved habitat protection is required to conserve stocks.

Resumen El río San Pedro y el río La Pasión se encuentran dentro de la cuenca del río Usumacinta, un centro de diversidad de peces de agua dulce de importancia mundial. Ambos ríos figuran entre las 50 regiones principales de América Central para conservar la biodiversidad de agua dulce. Este estudio presenta un listado actualizado de 70 especies de peces, de las cuales 6 son especies no nativas para la cuenca del Río Usumacinta. De estas especies, 69 se reportan para el Río La Pasión y 56 para el río San Pedro, lo que representa una riqueza de especies más alta que la reportada previamente. La lista de verificación se deriva de un muestreo sistemático de peces realizado en 2019 y registros disponibles en bases de datos públicas y literatura publicada. El 78% de las especies se reportan en ambos ríos, siendo Cichlidae y Poeciliidae las familias con mayor riqueza. Las especies con mayor fidelidad en Río La Pasión fueron el bagre acorazado Pterygopichthys spp. y el pez vivíparo Gambusia sexradiata; y los cíclidos Thorichthys meeki y Oscura heterospila tuvieron mayor fidelidad en el Río San Pedro. Thorichthys helleri se distribuyó ampliamente en ambos ríos. Según la Lista Roja de Especies Amenazadas de la UICN, existen cuatro especies clasificadas como Vulnerable en el Río La Pasión. Sin embargo, el 62 % de las especies son de Preocupación Menor, el 25 % de las especies tienen Datos Insuficientes y el 6 % se enumeran como No Evaluadas. Se necesita más investigación para documentar el estado de la fauna de peces, y se requiere una mejor protección del hábitat para conservar las poblaciones.

RESUMO

Abstract This study presents a survey of small-stream fish species from the Purus-Madeira interfluve, collected in four streams near Humaitá on the highway BR-319. The results reveal a rich and diversified ichthyofauna with 3016 collected individuals distributed in 84 species, six orders, 25 families, and 60 genera. Of all the specimens collected, the Characiformes was the most representative, with eight families, 26 genera, and 42 species, followed Siluriformes, with nine families, 20 genera, and 23 species. In terms of families, Characidae had the highest number of species (25), followed by Loricariidae (9), and Cichlidae (8). Among the 95 captured species,s 11 are the first records for the region, evidencing a high diversity in these environments. Of the 84 species recorded in this study, 15 have not been assessed by the IUCN, while the remaining 62 include 23 listed as Least Concern (LC), three as data deficient (DD), and one as Near Threatened (NT). The southeastern Amazon region still has few fish surveys, especially in the region comprising the Purus-Madeira Interfluve, which highlights the importance of surveys to fill gaps and understand the biodiversity distribution patterns in the region.

Resumo Este estudo apresenta um levantamento das espécies de peixes de pequenos riachos do interflúvio Purus-Madeira, coletadas em quatro riachos perto de Huimaitá na rodovia BR-319. Os resultados revelam uma ictiofauna rica e diversificada com 3016 indivíduos distribuídos em 84 espécies, seis ordens, 25 famílias e 60 gêneros. De todos os espécimes coletados, Characiformes foi a mais representativa, com oito famílias, 26 gêneros e 42 espécies, seguida da Siluriformes, com 9 famílias, 20 gêneros e 23 espécies. Em termos de famílias, Characidae apresentou o maior número de espécies (25), seguida de Loricariidae (9) e Cichlidae (8). Dentre as espécies capturadas, do total de 84 espécies, 11 são o primeiro registro da região, evidenciando uma alta diversidade nesses ambientes. Das 84 espécies registradas neste trabalho, 15 não foram avaliadas pela IUCN, 63 listadas como Menos Preocupante (LC), quatro como Deficientes em Dados (DD) e uma como Quase Ameaçada (NT). A região sudoeste da Amazônia ainda conta com poucos levantamentos de peixes, principalmente na região que compreende o Interflúvio Purus-Madeira, por isso é importante realizar levantamentos para preencher lacunas de coletas e compreender padrões de distribuição da biodiversidade da região.