A família Potamotrygonidae forma um clado monofilético com três gêneros: Paratrygon Duméril, Potamotrygon Garman e Plesiotrygon Rosa, Castello & Thorson. A maioria das espécies dessa família possui distribuição restrita a uma única bacia ou sistema fluvial, e somente as espécies Potamotrygon motoro, Potamotrygon orbignyi e Paratrygon aiereba estão presentes em mais de uma bacia hidrográfica. O presente estudo teve como objetivo investigar a estrutura genética de Paratrygon aiereba em alguns rios da região Amazônica: Negro, sistema Solimões-Amazonas, Tapajós, Xingu, e Araguaia. Para tal foram utilizados como marcador molecular os genes de ATPase subunidade 6, e COI. As análises com o fragmento de COI indicaram que o gênero Paratrygon é grupo irmão dos outros gêneros da família potamotrygonidae. Os resultados para o fragmento de ATPase mostraram que essas populações estão estruturadas dentro dos rios, com fluxo gênico restrito, ou mesmo sem fluxo gênico, apresentando uma correlação positiva entre distância genética e distância geográfica. Paratrygon aiereba é composta por três clados com distância genética de pelo menos 2%. A divergência encontrada dentro desse grupo é semelhante à observada entre Potamotrygon spp. Segundo as premissas para barcoding COI e a distribuição alopátrica de três clados em P. aiereba indicam que esse grupo pode ser um complexo de espécies. O rio Negro é conhecido por sua pesca ornamental, e na calha Solimões-Amazonas, esses animais são utilizados como fonte de proteína e sofrem com a pesca comercial. Em vista disso medidas de conservação para esta espécie devem ser tomadas em nível local, considerando cada rio separadamente, ao invés de empregar escalas regionais maiores.

The family Potamotrygonidae is monophyletic comprising three genera: Paratrygon Duméril, Potamotrygon Garman and Plesiotrygon Rosa, Castello & Thorson. The distribution of most species in this family is restricted to a single basin or fluvial system. Only Potamotrygon motoro, Potamotrygon orbignyi and Paratrygon aiereba are found in more than one river basin. In this study we investigate genetic structuring of Paratrygon aiereba, from five rivers of the Amazon region: Negro, Solimões-Amazon-Estuary system, Tapajós, Xingu and Araguaia. Sixty-three individuals were sequenced for ATPase 6, and a representative subsample of 27 individuals was sequenced for COI. The COI dataset analysis indicated that Paratrygon is sister to all other potamotrygonid genera and species. Population parameters inferred from the analysis of ATPase 6 sequences revealed that the populations of this species are structured within each river, with no or nearly non-existent gene flow occurring between rivers and a positive correlation between geographic and genetic distances. Paratrygon aiereba is comprised of three geographically restricted clades with K2P interclade distances of at least 2%. Intraspecific divergence within P. aiereba is similar to the interspecific divergence observed in Potamotrygon spp. sampled throughout the same geographic area. Using the premises of COI barcoding and the allopatric distribution of the three P. aiereba clades, the taxon P. aiereba most likely comprises three distinct biological species. Since freshwater stingrays of the family Potamotrygonidae are highly exploited for the aquarium trade, management and conservation strategies need to be implemented at the level of each river basin, rather than at the level of the Amazon basin.

DNA barcoding is a recently proposed global standard in taxonomy based on DNA sequences. The two main goals of DNA barcoding methodology are assignment of specimens to a species and discovery of new species. There are two main underlying assumptions: i) reciprocal monophyly of species, and ii) intraspecific divergence is always less than interspecific divergence. Here we present a phylogenetic analysis of the family Potamotrygonidae based on mitochondrial cytochrome c oxidase I gene, sampling 10 out of the 18 to 20 valid species including two non-described species. Potamotrygonidae systematics is still not fully resolved with several still-to-be-described species while some other species are difficult to delimit due to overlap in morphological characters and because of sharing a complex color patterns. Our results suggest that the family passed through a process of rapid speciation and that the species Potamotrygon motoro, P. scobina, and P. orbignyi share haplotypes extensively. Our results suggest that systems of identification of specimens based on DNA sequences, together with morphological and/or ecological characters, can aid taxonomic studies, but delimitation of new species based on threshold values of genetic distances are overly simplistic and misleading.

Peixes adultos da espécie Eugerres brasilianus (Gerreidae) tiveram suas brânquias analisadas em microscópio eletrônico de varredura. O epitélio de revestimento é uniforme em todas as porções dos arcos. É formado por células com micropregas concêntricas principalmente nas lamelas primárias e na região faríngea, locais onde são abundantes as células que secretam muco. A caracterização ultra-estrutural das brânquias de E. brasilianus indica que a espécie não é filtradora e que em sua alimentação deve predominar a ingestão de pequenos organismos. Esses resultados estão de acordo com os dados da literatura que determinam o hábito alimentar da espécie através de análises de conteúdo estomacal e outros aspectos.

The gills of the adult fish, Eugerres brasilianus (Gerreidae) were analyzed in a scanning electron microscope. The stratified epithelium was uniform on all parts of the branchial arch. Concentric microridges were present on cells that form this epithelium and were mainly observed in the primary lamellae and pharyngeal region where mucous cells were also abundant. The ultrastructural features of E. brasilianus gills indicated that this was not a filtering species, and that the feeding habit included mainly the intake of small organisms. The results presently obtained agreed with other literature data which determined the feeding habit of this species by means of stomach content analysis and other aspects.

Gills arches of the freshwater fish Prochilodus scrofa Steindachner, 1881 (Lt= 8.0-12.4cm) were removed to be analyzed in a scanning electron microscope. The morphology of the superficial structures of the gill filaments and pharyngeal region of the gills arches was discussed and related to their functional aspects. A great quantity of mucous secretory cells and of microridges, along with the pavement cell surface of the primary lamellae and branchial pharyngeal region, indicate the existence of a protection strategy of the respiratory lamellae. The chloride cells are abundant, specially on the distal portion of the primary lamellae, and bring out the osmo regulatory capacity of this species. This fish seems not to be a filtering one according to: its short and simple gill rakers; presence of several taste buds turned towards the mouth opening; evidence of spines on the external side of the arches and an abundant secretion of mucous in the pharyngeal region. This species probably selects the food to be swallowed through its chemical receptors and retains it with the help of spines and mucous secretion this way protecting the gills filaments against the rubbing of particles over them.