Luiz Roberto Malabarba

Axillary and pectoral-fin spine glands play a central role in the defensive biology of Siluriformes by releasing toxic secretions; however, their distribution, structural diversity, and evolutionary significance within Corydoradinae remain poorly understood. Here, we present the first comparative histological analysis of these glands across seven genera of Corydoradinae. Axillary glands were present in all examined genera and exhibited a conserved lobular organization consistent with a holocrine secretion type as described previously in other Siluriformes. In contrast, venom-associated pectoral spine glands were restricted to a clade comprising Hoplisoma, Brochis, and Osteogaster. In these genera, gland position and cellular morphology closely match venom glands described in other siluriform lineages, supporting a lineage-specific derived condition. Conversely, Corydoras, Aspidoras, Scleromystax, and Gastrodermus lacked true venom-associated pectoral spine glands and instead displayed abundant epidermal granular cells and club cells, consistent with the retention of a non-venomous ancestral state. This pattern is congruent with phylogenetic relationships and implies that mimicry rings may involve Müllerian, quasi-Batesian, and Batesian components depending on their species composition and the degree of defense exhibited by the species present.

The genus Odontostilbe (Characiformes: Characidae) comprises small Neotropical characids widely distributed across South American river basins. Specimens previously identified as Odontostilbe paraguayensis are revised and a new species is described from the upper rio Paraná basin. Species delimitation is based on morphological, meristic, and morphometric characters. The new species differs from most congeners by the combination of an incomplete lateral line, presence of mesopterygoid teeth arranged in two distinct groups, and the presence of hooks on all unbranched anal-fin rays in mature males. Odontostilbe paraguayensis is distinguished from all congeners by the presence of partially fused supraneurals forming a distinctive predorsal structure. The distribution of O. paraguayensis is restricted to the rio Paraguay basin, whereas the new species occurs in the upper rio Paraná basin. These results refine the taxonomic limits within Odontostilbe and contribute to a better understanding of species diversity and distribution patterns in the La Plata drainage. A key to identification of the species of Odontostilbe from Paraná-Paraguay basin is provided.

Specimens referred to Jenynsia (Plesiojenynsia) unitaenia from the Tramandaí-Mampituba ecoregion were genetically compared in order to obtain their phylogeographic relationships. Molecular analysis estimated that populations from rio Mampituba and rio Araranguá diverged from rio Maquiné and rio Três Forquilhas populations during the Pleistocene (about 1.2 million years ago). Further, morphological analysis allowed the diagnosis of these two lineages based on the color pattern, as is common among the species of the subgenus Plesiojenynsia. Thus they are referred to as separate species: Jenynsia unitaenia restricted to the rio Araranguá and rio Mampituba, and a new species from rio Maquiné and rio Três Forquilhas. The pattern of historical relationships of these species of Jenynsia among Tramandaí-Mampituba ecoregion drainages differs from those described for other endemic fish taxa.

Brazil hosts the highest fish diversity globally, underscoring the critical role of Brazilian Scientific Fish Collections (BSFCs) in biodiversity research and conservation. Despite their importance, BSFCs face persistent challenges. This study introduces the CARDUME network, the first nationwide initiative to assess BSFCs and propose strategies to enhance their role in ichthyology. Data from 74 collections across 25 Brazilian federal units reveal that most are affiliated with public universities and house 8 502 992 catalogued specimens in 906 890 lots, including over 2600 primary types. Although digitization efforts are underway in 92% of BSFCs, only 37% currently share data online. Genetic resources are severely limited, with tissue samples available for just 3% of specimens. Significant funding disparities exist, with 70% of collections receiving less than USD170 annually. Gender inequality is also notable, with more male-curated than female-curated collections. Survey responses highlighted issues such as staff shortages, inadequate facilities, and limited resources for fieldwork and collection curation. CARDUME aims to address these gaps through ­collaboration, professional training, improvement of data quality, and increase of shared data, while also advocating for recognition by Brazilian institutions, funding agencies, and the government. O resumo em português está disponível no material suplementar.

Gymnogeophaguslabiatus and G. lacustris represent a pair of sister taxa distributed in the Patos Lagoon (ELP) and Tramandaí-Mampituba (ETM) ecoregions in Southern Brazil and Uruguay. While G. lacustris was traditionally considered endemic to the ETM, G. labiatus has been assigned to both ecoregions, being distinguished from G. lacustris by its hypertrophied lips, which represent an adaptation for foraging in rocky environments, and by the variation in coloration. A recent study using mtDNA and morphological data challenged this interpretation and suggested that G. labiatus is exclusive of ELP, and that all individuals in ETM should be considered G. lacustris. In this work we used genome-wide ddRADseq markers to evaluate the evolutionary relationships between these species. The results corroborated early findings that each ecoregion harbors an independent evolutionary lineage, and that all individuals in ETM correspond to G. lacustris. Our results do not show significant genetic structure between riverine and lacustrine populations in ETM. However, we found evidence for secondary contact between G. labiatus and the riverine population of G. lacustris, suggesting that the hypertrophied lips in both groups may have a common genetic background, and may indicate an instance of adaptive introgression.

Males of Rachoviscus crassiceps have two small longitudinal black marks on pectoral-fin rays associated to hard and thick tissues that develop in the dorsal surface of the first and second branched pectoral-fin rays, covered dorsally with pheromone secretion club cells. Besides that, the interradial membrane between the second and third and sometimes that between the third and fourth branched pectoral fin rays are thicker than between other contiguous rays, and covered ventrally with hypertrophied mucous cells. Courtship signaling is essential for mate recognition and is frequently multimodal. Courtship signals are apparently essential for mate recognition in inseminating characiform species of the families Characidae and Stevardiidae, that show more conspicuous or more developed courtship signals than in external fertilization species. We propose the pectoral fin organ in the inseminating acestrorhamphid R. crassiceps of the subfamily Thayeriinae constitutes a putative multicomponent courtship signal, including chemical (pheromones) and visual signals (black mark on pectoral fin).

In a recent study based on the generalized mixed Yule coalescent method for delimiting species, a threshold of 2% genetic distance using cytochrome c oxidase subunit I sequences was used to delimit the species of Microglanis. That action resulted in assembling several populations of Microglanis from Atlantic coastal rivers between Rio Grande do Sul and São Paulo states as a single species, Microglanis cottoides, including Microglanis cibelae as a junior synonym. We reexamined these populations and found three species diagnosed by their morphology and that constitute separate mtDNA lineages, including a new species. The synonym of M. cibelae and M. cottoides is reviewed and refuted based on morphological and molecular evidence. M. cibelae and the new species are sympatric and occasionally syntopic in the Tramandaí, Mampituba, and Araranguá river basins. The new species is distinguished from M. cibelae and M. cottoides by the anterior margin of the posttemporosupracleitrum narrow articulated with the epioccipital, the short mental and maxillary barbels, and depressed head and body.

Diapoma pampeana was recently described to occur in the upper Negro basin in Uruguay and Brazil. An isolated population tentatively identified as D. pampeana from the Pando stream, a perturbed coastal drainage in Uruguay, is studied and compared under the light of morphological and molecular data to test if there is evidence to consider it as a separate species. New geographical records for the species are presented and included in the comparisons. The specimens analyzed were pooled into four groups: Pando, Santa Lucía, Middle Negro and Upper Negro. We analyzed 32 morphological characters using statistical procedures and recovered a COI-based phylogeny of different populations of D. pampeana to test if they may represent different species. Size-corrected PCA revealed that the Pando and Upper Negro groups are greatly diverging in both morphometric and meristic data along PC1 (mainly by the snout to dorsal-fin origin, dorsal to adipose-fin origins, number of longitudinal scales and predorsal scales). This deviating pattern was also obtained in a cluster analysis. The Santa Lucía and Middle Negro groups were found to be intermediate morphotypes. In contrast, molecular analyses revealed that the Pando and Upper Negro specimens resemble genetically and, thus, are placed together in the Neighbor-joining and Bayesian topologies, as part of a monophyletic Diapoma. We proposed that the Pando population, despite its deviating morphology observed, can be classified as D. pampeana. Therefore, this population constitutes a remarkable example of an isolated population that is morphologically divergent but genetically similar to the geographically most distant conspecific population.

The integration between morphological and barcode datasets allowed the discovery of new populations of Psalidodon cremnobates, expanding the distribution of this species to the Mampituba River drainage, municipality of Cambará do Sul, Rio Grande do Sul, Brazil and letting a review of the classification of extinction risk. DNA barcoding for these populations and other of the “Psalidodon scabripinnis complex” living in swift currents further supports the recognition of Psalidodon brachypterygium (new combination), P. cremnobates and P. laticeps as distinctive species, regardless of the lack of discrete and diagnosable ranges in body counts and measurements among them. Barcode DNA, in this sense, helps in recognizing monophyletic lineages and determining the boundaries between species with similar morphologies. The barcode divergence recommended to recognize species is also discussed.