Adaptive radiations are typically triggered when a lineage encounters a significant range of open niche space (ecological opportunity), stemming from colonisation of new areas, extinction of competitors or key innovations. The most well-known of these is the colonisation of new areas, through either dispersal into new regions or the invasion of novel ecological regimes. One aspect of ecological opportunity that has rarely been studied, however, is the extent to which pre-existent competitors act to limit diversification in newly colonised adaptive zones. Herein, we show that in multiple geographically independent invasions of freshwaters by marine Sea Catfishes (Ariidae), rates of both morphological disparification and lineage diversification are inversely related to the presence and diversity of other freshwater fish lineages. Only in one region (Australia-New Guinea) with an otherwise depauperate freshwater fauna, has an ariid invasion gained any substantial traction. This is true at both regional and community scales, suggesting that competitive constraints may be an important factor regulating adaptive radiation.

Ariid monophyly and intrafamilial relationships are investigated based on cladistic analysis of 230 morphological characters. Terminal taxa examined include whenever possible type‐species, or the most morphologically similar species to the type‐species of the nominal genera, and the largest possible number of species, including cleared and stained specimens, available in zoological collections. Previous hypotheses about monophyly of the Ariidae are strongly corroborated by new synapomorphies discovered in the present study. The subfamily Galeichthyinae and the remaining ariids are strongly supported by new morphological characters. The monotypic subfamily Bagreinae is recognized as the sister group to all nongaleichthyin ariids, supported by a large series of exclusive synapomorphies. A new concept of Ariinae is presented: the subfamily is found to be unequivocally monophyletic and includes all ariid genera, except Galeichthys and Bagre. New data supporting the monophyly of the genera included in the Ariinae are introduced and previous hypotheses of monophyly, species composition, morphological definition, and relationships are reviewed and discussed.

Coastal and marine environments are characterized by a lack of evident physical barriers or geographic isolation, and it may be difficult to understand how divergence can arise and be sustained in marine environments. The identification of 'soft' barriers is a crucial step towards the understanding of gene flow in marine environments. The marine catfishes of the family Ariidae are a demersal group with restricted migratory behavior, no pelagic larval stages, and mechanisms of larval retention, representing a potentially useful model for the understanding of historical processes of allopatric speciation in the marine environment. In the present study, two lineages of the Coco sea catfish, Bagre bagre, were recognized from their complete segregation at both mitochondrial and morphological levels. One lineage is distributed between Venezuela and the northern coast of Brazil, including the semiarid northeast coast, while the second lineage is found on the eastern coast of Brazil, including the humid northeast coast. Based on distribution area, habitats preference, and genetic variability, inferences are made in relation to biogeography and demography of lineages in Atlantic coast of South America.Ambientes marinhos costeiros são caracterizados pela falta de barreiras físicas evidentes e ausência de isolamento geográfico, sendo difícil compreender como diferentes linhagens podem surgir e ser mantidas nestes ambientes. A identificação de barreiras permeáveis é um passo importante para a compreensão do fluxo gênico em ambientes marinhos. Os bagres marinhos da família Ariidae são um grupo demersal, com mecanismos de retenção larval e sem comportamento migratório ou estágio larval pelágico, representando um grupo potencialmente útil para a compreensão de processos históricos de especiação alopátrica no ambiente marinho. No presente estudo, duas linhagens do bandeirado ou bagre de fita, Bagre bagre, são reconhecidas com base na completa segregação mitocondrial e morfológica. Uma linhagem é encontrada da Venezuela à costa norte do Brasil, incluindo a costa nordeste semi-árida, enquanto a segunda linhagem é encontrada na costa leste e sudeste do Brasil, incluindo a costa nordeste úmida. Com base na área de distribuição, habitat preferencial e a variabilidade genética, inferências são feitas em relação à biogeografia e demografia das duas linhagens na costa do Atlântico da América do Sul.

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The tropical western South Atlantic, which includes a substantial portion of the Brazilian Exclusive Economic Zone, is a region of endemism broadly recognized as being of prime importance for the conservation of the marine biodiversity. The north coast of Brazil, which comprises the states of Amapá, Pará and Maranhão from the mouth of the rio Oiapoque to the mouth of the rio Parnaíba, harbors the largest continuous mangrove in the world, with approximately 8,900 km2. The high discharge of freshwater and continental sediments in the delta of the Amazonas affects the regime of tides, ocean currents, and several oceanographic processes of the north coast, with direct impact on the composition of the biota found in the region. Despite its economic value and intrinsic biological relevance, several aspects of the diversity of the marine and estuarine fishes of the region are poorly known. This situation results mainly from a historical imbalance in terms of the number of studies devoted to increasing the knowledge of the marine biota along the Brazilian coast, such as those dealing with species inventory and taxonomic revisions, which are typically concentrated in the south and southwestern portions of the country. The scientific production focused on marine organisms of the north coast is also imbalanced, and reflects the relatively small number of taxonomists and research groups working on that subject. The insufficient knowledge of the biodiversity of the marine and estuarine fishes of the north coast is an impediment to the implementation of adequate public policies aimed at the management of natural resources in the region. In the long term, that situation is potentially harmful in terms of conservation of a still poorly known biota. A better understanding of the marine fish fauna of the north coast of Brazil will be achieved only through the investment in scientific research and personnel training in systematics and biogeography, coupled with the modernization of the current infrastructure and expansion of scientific collections of the region.

The Brazilian North coast is one of the world’s most important shrimp fishery grounds, with a total area of approximately 223,000 km2. However, the available data on the diversity of fish caught by the region’s industrial trawler fleet are limited to the commercially-valuable species. This lacuna in the data on the region’s marine fish fauna is worrying, both for the management of stocks and the conservation of the local biodiversity. The present study was based on a comprehensive inventory of the teleost fishes captured by the industrial outrigger trawling operations off the North coast of Brazil. This inventory recorded 201 species belonging to 64 families and 20 orders, and revealed a unique fauna, characterized by 17 endemic species, and a mixture of estuarine-dependent and marine species, mainly associated with coral reefs. The Kernel density analysis indicated that the industrial trawling fleet operates within an important ecotone, which encompasses the transition zones of different fish communities found off the Brazilian North coast.

The sciaenid genus Bairdiella comprises a group of relatively small fishes found in inshore waters and estuaries of the western Atlantic and eastern Pacific. Despite recent analyses of the phylogenetic relationships of Bairdiella, there has been no comprehensive revision of the alpha taxonomy of the species of the genus. Bairdiella ronchus from the western Atlantic, has a complex taxonomic history, with four junior synonyms recognized. Based on morphological and molecular evidence, this study indicates that B. ronchus represents a species complex. The species is therefore redescribed and its geographic range is redefined. Bairdiella veraecrucis, which is currently recognized as a junior synonym of B. ronchus, is revalidated, and a new species of the genus is described from the Atlantic coast of Brazil. Finally, inferences are made on the diversity and biogeography of the B. ronchus species complex.

Variation in the pattern of the vomero-palatine tooth patches of Genidens barbus and Genidens machadoi is reviewed and the species redescribed based on the analysis of 46 morphological characters. Genidens machadoi can be distinguished from INTRODUÇÃO Os bagres marinhos Genidens barbus (Lacépède, 1803) e Genidens machadoi (Miranda-Ribeiro, 1918a) são espécies de grande porte (chegando a atingir 1.200 mm e 700 mm de comprimento, respectivamente), que ocorrem nas regiões sudeste e sul do Brasil. As duas espécies são bastante comuns e juntas representam, em número de indivíduos, mais de 80% da categoria "Bagres" (= Ariidae) desembarcada pela frota pesqueira comercial que opera na região sudeste do Brasil (Marceniuk et al., 1995).As espécies da família Ariidae do sudeste e sul do Brasil são usualmente diferenciadas com base na forma das placas de dentes da região do palato. Durante trabalho de identificação das espécies que compõem a categoria "Bagres", foram reconhecidos padrões das placas de dentes, a priori atribuídos a Genidens barbus, que relacionados com outras características do crânio, permitem o reconhecimento de uma espécie distinta. A revisão dos nomes disponíveis e o exame do exemplar-tipo de Tachysurus machadoi Miranda-Ribeiro, 1918a, mostraram que Genidens machadoi é o nome aplicável a esta outra espécie identificada.