Abstract A new species of Moenkhausia is described from a tributary of the rio Teles Pires, upper rio Tapajós basin, Serra do Cachimbo, Pará State, Brazil. The new species is diagnosed by a distinctive body coloration pattern consisting of dark blotches on the anterior portion of scales of the second to seventh longitudinal series, a conspicuous horizontally elongate, drop-shaped blotch on the caudal peduncle, and a unique eye coloration in life, with the dorsal portion of the iris reddish and the ventral portion bright golden, as well as five or six branched pelvic-fin rays. The new species is morphologically similar to a group of Amazonian congeners that share unusual body coloration and colored eyes in life, all of which exhibit restricted distributions associated with upland areas of the Brazilian crystalline shield. This new taxon represents the fifth species of this putative group described from the Serra do Cachimbo, whose members are likely endemic to the region, indicating that the Serra do Cachimbo may represent an important region of endemism for small-bodied freshwater fishes and underscoring the need for continued taxonomic and biogeographic studies in Amazonian shield headwaters.
Abstract 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.
Abstract Seasonal reproduction in teleost fishes is modulated by interactions among environmental, physiological, and endocrine factors. This study investigated the environmental modulation of oogenesis in the Neotropical potamodromous fish Prochilodus magdalenae (bocachico) across natural (Swamp and River) and aquaculture environments. Oogenesis was analyzed histologically, plasma estradiol (E2) concentrations were quantified, and seven environmental variables including water physicochemistry and photoperiod, were monitored over approximately one and a half reproductive cycles. In the Swamp, oogenesis progressed from primary growth to advanced vitellogenesis during the low-rainfall period, whereas in the River, oogenesis advanced to mature and spawning stages during the rainy season. Under aquaculture conditions, ovaries reached advanced vitellogenesis but failed to reach mature or spawning stages. E2 concentrations peaked during advanced vitellogenesis in natural and aquaculture females. Principal component analysis (PCA) and generalized additive models (GAM) indicated that oogenesis was shaped by multiple drivers. The first two PCA axes explained 78.8% of environmental variation, while the GAM explained 45.3% of the deviance in ovarian stage. A second GAM explained 79% of the deviance in E2 concentrations. Overall, oogenic progression depended on non-linear interactions among variables, seasonal dynamics, and habitat type, highlighting the sensitivity of oogenesis in P. magdalenae to environmental variability.
Abstract A new species of anostomid endemic to the Xingu River basin, Brazil, is described. Originally discovered during ecological surveys in the Volta Grande do Xingu, the species is formally recognized based on an integrated analysis of external morphology, osteology, and molecular data. Sixty specimens were examined, including cleared and stained material. Diagnostic features include eight elongated horizontal midlateral blotches, 14 transverse dorsal bars, three premaxillary teeth and four dentary teeth, 16 scale rows around the caudal peduncle. Osteological examination revealed fused fourth and fifth infraorbitals and a small ventral expansion of the antorbital, latter not previously documented in other anostomids. Species delimitation methods (ASAP and PTP) using DNA barcoding consistently supported the new species as a distinct lineage, with genetic distances ranging from 2 to 3% relative to the closest congeners (L. nigrotaeniatus, L. vanzoi, L. unitaeniatus, L. sidlauskasi). The species inhabits shallow rapids with rocky and sandy substrates, feeding predominantly on aquatic insect larvae, supplemented by benthic invertebrates, and plant material. Despite environmental pressures from hydropower development and mining, the new species is widely distributed in the basin and is suggested as Least Concern (LC) under IUCN criteria.
Abstract Based on an integrative approach (genetic, morphology and biogeography), two new species of Acantholebias are described from Laguna de Rocha and middle Cebollatí River basins respectively (Laguna dos Patos ecoregion). The new species from Laguna de Rocha is diagnosed by a chromatic character and cytochrome b mutations; the new species from middle Cebollatí is diagnosed by a combination of chromatic and squamation patterns. Both species are allopatrically distributed relative to the other species of the genus and to each other. This study also indicates that Acantholebias quirogai presents high chromatic polymorphism that could be related to drainage rearrangements between the Lower Uruguay and Laguna dos Patos ecoregions.
