Explore the vast range of titles available.

Aim: To present an updated database of fish species recorded on south-western Atlantic reef environments and to explore the ecological drivers of the structure, the latitudinal gradient of biodiversity and the centre of endemism in this peripheral province. Location: South-western Atlantic (SWA): Brazilian and Argentinian Provinces. Methods: A database composed of 733 fish species along 23 locations in the SWA (00°55' N to 43°00' S) was compiled based on primary data, literature and museum records. Cluster and beta diversity analyses were carried out to evaluate faunal overlaps among locations and subprovinces. \"Target-area-distance effect\" and \"stepping stones dispersal\" hypotheses for assemblage composition were tested through Mantel tests. Relationships between the distribution patterns and ecological traits of reef fish species were investigated through generalized linear mixed-effect models. Results: Out of the 733 fish species, 405 are SWA resident reef fishes, of which 111 (27%) are endemics and 78 are threatened with extinction. Cluster analysis detected six subprovinces in the SWA structured following the target-area-distance model, and with no evidence for a latitudinal gradient in diversity. The greatest overall richness and endemic species richness were found in the east-south-eastern region. Depth range, habitat use and body size were the main drivers of SWA reef fish assemblage structure. Main conclusions: The Brazilian and Argentinian coasts constitute different provinces structured by oceanographic barriers and environmental filters. Similarities among oceanic islands indicate connectivity driven by stochastic and ecological factors. Species richness and endemism indicate that peripheral provinces may also bear centres of origin and biodiversity, patterns driven by parapatric/ecological speciation and the overlap between tropical and subtropical reef fish species. Ecological drivers of reef fish distribution, such as habitat specialization and body size, support hypotheses of speciation in the periphery. New approaches for spatial planning, marine protected areas and off-reserve marine management are essential for the conservation and sustainability of SWA reef fishes.

The Gymnotiformes, or electric knifefishes, is a clade of freshwater ostariophysan fishes native to tropical South and Central America that are easily recognized by the presence of an elongate body and elongate undulating anal fin, and lack of dorsal and pelvic fins. In this study, we report on unusual specimens of the Black Ghost Knifefish Apteronotus albifrons (Apteronotidae) exported from Asian aquaculture facilities, which exhibit a fin located on the median dorsal surface. This fin exhibits the distinctive ball-and-socket articulating joint between the fin rays and pterygiophores otherwise only observed in gymnotiform anal fins and differs from the laterally restricted dorsal-fin-pterygiophore articulation of other ostariophysan taxa. We interpret the dorsally located fin of these specimens of Apteronotus albifrons as an ectopic expression of a median fin with an anal-fin phenotype and do not interpret the dorsally located fin as representing the reappearance of the plesiomorphic ostariophysan dorsal fin. The anterior–posterior position of the dorsally expressed fin corresponds closely with that of the dorsal organ, a fleshy electroreceptive structure that lies along the dorsal body margin of other apteronotids. This topological concordance implies the presence of a conserved embryonic tissue underlying development of both the dorsal organ and the dorsally expressed median fin.

The Neotropical freshwater fish (NFF) fauna constitutes the most diverse continental vertebrate assemblage on Earth, with more than 6,345 species distributed across South America, Central America, and the Greater Antilles. These species display a bewildering array of ecophysiological and behavioral traits, or ecotraits , used to exploit habitat and food resources across geographical, climatic, and seasonal gradients. Despite intensive taxonomic and systematic studies, the literature on ecological preferences and tolerances of NFF species is scattered and incomplete, and we have previously lacked a centralized database. Here we present the first comprehensive dataset of ecotraits for the NFF fauna using published data and expert knowledge from the community of Neotropical ichthyologists. This ecomatrix includes adult modal values for 42 ecotraits scored for all valid NFF species, including body size, four of habitat utilization related to water chemistry, 21 of physical habitat structure, 10 of diet (i.e. trophic guilds), and six other behavioral traits. This ecomatrix is a foundation for future studies on the ecology and conservation of Neotropical aquatic biodiversity.