o tamanho máximo atingido por estes peixes varia de 30 centímetros a 18 metros. Na maioria, o desenvolvimento do embrião é ovovivíparo; alguns são vivíparos (como Prionace glauca) e poucos são ovíparos (no Brasil, apenas os da família Scyliorhinidae) . São todos carnívoros e marinhos, com exceção de Carcharhinus leucas, que entra em água doce. Vivem desde águas costeiras até em alto-mar, tanto no fundo como na superfície. Certas espécies já foram capturadas a grandes profundidades. No Brasil muitas espécies são utilizadas como alimento. São pescadas com espinhéis e redes de espera. Os cações oceânicos de grande porte são pescados por barcos atuneiros. Em todos os mares são conhecidas cerca de 250 espécies.As raias diferem dos cações principalmente por possuir 5 pares de fendas branquiais na região ventral do corpo. Este é caracteristicamente achatado, com as nadadeiras peitorais muito desenvolvidas, formando um disco; as nadadeiras dorsais e a caudal são reduzidas ou estão ausentes; não há nadadeira anal. Atrás de cada olho há uma fenda denominada espiráculo, ligada à câmara branquial e servindo de entrada a pelo menos parte da água que banha as brânquias.Nos cações há às vezes um espiráculo reduzido. O tamanho máximo alcançado pelas raias varia de 15 centímetros a 7 metros de largura. Quase todas são ovovivíparas; no Brasil, apenas as da família Rajidae são ovíparas. Seu alimento básico é constituído de invertebrados marinhos, principalmente moluscos e crustáceos. A maior parte das espécies habita o fundo, onde muitas vezes estes animais se enterram. Algumas, de vida mais ativa, têm hábitos pelágicos.Apenas uma família, Potamotrygonidae, vive exclusivamente em água doce.Todas as outras são marinhas, mas algumas espécies de peixe-serra (Família Pristidae) entram nos grandes rios, como é o caso de Pristis perotteti no Rio Amazonas. De modo geral, as raias não são apreciadas como alimento no Brasil. Conhecem-se cerca de 340 espécies no mundo.As quimeras, peixes da Subclasse Holocephali, formam um grupo pequeno, de aproximadamente 20 espécies. Caracterizam-se pela abertura branquial única, pela curiosa probóscida e pelo espinho móvel na frente da primeira nadadeira dorsal. Não possuem espiráculos e a entrada de água para as brânquias faz-se através das fendas nasais, conectadas com a cavidade da boca.O tamanho máximo das espécies varia de 60 centímetros a 2 metros de comprimento. São peixes exclusivamente marinhos, que vivem em águas um pouco afastadas da costa, alimentando-se basicamente de moluscos. As quimeras são ovíparas. Os machos possuem um tubérculo espinhoso móvel na região anterior e um apêndice retrátil na frente de cada nadadeira pélvica, com a função provável de segurar a fêmea durante o acasalamento. cm i SciELO/MZUSP 13 14 15 16 17 lí 19
Abstract:The fish species living in the freshwaters of the São Paulo state (393) are distributed among four major river basins: upper Paraná, Paraíba do Sul, Ribeira de Iguape and a set of small coastal drainages flowing directly into the Atlantic Ocean. Since these river basins drain areas with distinct vegetation types, soils, etc., each one has a different species composition. In the Upper Paraná the large Rio Paraná and some of its large tributaries (Tietê, Paranapanema, and Grande) contain large species that support commercial fisheries, however, 70 to 80% of the ichthyofauna is composed by small species found in small streams, including those in headwaters where many are endemic. The inventory of the ichthyofauna greatly benefited from three research projects supported by the BIOTA/FAPESP program, but much work remains to be done to collect and describe new species from areas such as deep channels, headwaters and marginal and swampy áreas around ponds and man-made lakes and reservoirs. The ichthyofauna of the São Paulo State has suffered from deforestation, sewage, damming of rivers for construction of power plants, urbanization, etc., so that 66 species are currently considered threatened at various levels according to the criteria of the International Union for Conservation of Nature and Natural Resources (IUCN). Keywords: fresh water fishes, biodiversity of the State of São Paulo, BIOTA/FAPESP Program.
Nonnative fish introductions disrupt ecosystem processes and can drive native species to local extinction. Two of the most widespread, introduced species are the common carp (Cyprinus carpio) from Eurasia and the Nile tilapia (Oreochromis niloticus) from Africa. In North and South America, these introductions stem from aquaculture facilities, as well as historical introductions for recreational angling. An emergent field of ecological niche modeling provides robust predictions of the geographic potential of alien species to better understand their capacity to become established at broad scales. We used this modeling approach to produce spatially explicit predictions of the invasive potential of common carp and Nile tilapia in the Americas. Model predictions were tested using occurrence data for established populations in their native area and in the Americas. Results indicated that predictive power of niche models was high. Distributional potential of common carp in the Americas covers most temperate regions and high mountain tropical aquatic systems, whereas that of Nile tilapia is focused in the tropics and coast areas. The consequences of the potential establishment of these exotic species can be profound on native aquatic faunas, particularly on highly diverse regions such as the Amazon Basin and central Mexico.
BackgroundFreshwaters are the most threatened ecosystems on earth. Although recent assessments provide data on global priority regions for freshwater conservation, local scale priorities remain unknown. Refining the scale of global biodiversity assessments (both at terrestrial and freshwater realms) and translating these into conservation priorities on the ground remains a major challenge to biodiversity science, and depends directly on species occurrence data of high taxonomic and geographic resolution. Brazil harbors the richest freshwater ichthyofauna in the world, but knowledge on endemic areas and conservation in Brazilian rivers is still scarce.Methodology/Principal FindingsUsing data on environmental threats and revised species distribution data we detect and delineate 540 small watershed areas harboring 819 restricted-range fishes in Brazil. Many of these areas are already highly threatened, as 159 (29%) watersheds have lost more than 70% of their original vegetation cover, and only 141 (26%) show significant overlap with formally protected areas or indigenous lands. We detected 220 (40%) critical watersheds overlapping hydroelectric dams or showing both poor formal protection and widespread habitat loss; these sites harbor 344 endemic fish species that may face extinction if no conservation action is in place in the near future.Conclusions/SignificanceWe provide the first analysis of site-scale conservation priorities in the richest freshwater ecosystems of the globe. Our results corroborate the hypothesis that freshwater biodiversity has been neglected in former conservation assessments. The study provides a simple and straightforward method for detecting freshwater priority areas based on endemism and threat, and represents a starting point for integrating freshwater and terrestrial conservation in representative and biogeographically consistent site-scale conservation strategies, that may be scaled-up following naturally linked drainage systems. Proper management (e. g. forestry code enforcement, landscape planning) and conservation (e. g. formal protection) of the 540 watersheds detected herein will be decisive in avoiding species extinction in the richest aquatic ecosystems on the planet.
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