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In the present work, we examined the morphology, dimensions, cytochemical staining reactions and ultrastructure of blood cells from three freshwater stingray species, Potamotrygon wallacei, Potamotrygon motoro and Paratrygon aiereba, living in the waters of the middle Rio Negro basin (Barcelos, Amazonas, Brazil). We identified erythrocytes, erythroblasts, thrombocytes and four types of leukocytes (basophils, heterophils, lymphocytes and monocytes) in the blood of these stingray species. In all the freshwater stingray species studied, the shapes and dimensions of these cells were similar to those of marine elasmobranchs. Positive PAS staining occurred in heterophils and thrombocytes, and weak staining occurred in lymphocytes and monocytes, while metachromasia only occurred in basophils. Positive Sudan Black B staining was observed in thrombocytes and lymphocytes, and weak staining occurred in heterophils. Basophils and heterophils were the only cells with positive bromophenol blue staining, while no peroxidase staining was observed in any of the four leukocyte types. This is the first study to establish the dimensions and cytochemical staining profiles of blood cells in Amazonian stingray species. Because these elasmobranch species are exported as ornamental fish to countries worldwide, this study can contribute to establishing standards for blood constituents that may be helpful in assessing the health and welfare of these fish in artificial systems.

This study analyzed sex steroid hormones and morphology of the reproductive tract in free-living adult males of the cururu stingray (Potamotrygon wallacei). These stingrays were captured during the transition between drought and rising waters in the middle Rio Negro basin, which coincides with the reproductive period (spermatogenesis and copulation) of this endemic species. Levels of the plasma steroid hormones testosterone (T), 17 β-estradiol (E2), and progesterone (P4), the gonadosomatic and hepatosomatic indices, as well as histological characteristics of the testis and epididymis were evaluated. Three reproductive maturational stages were observed: regression males, capable to reproduce males, and active males. Plasma T levels were increasing and parallel with the rising water period in the middle Rio Negro basin and were associated with the progress of spermatogenesis. This was not observed for E2, which did not vary significantly among the different reproductive stages. The high P4 concentrations in males in regression and males capable of reproducing appeared to regulate the progression of spermatogenesis. Increases in this hormone in the plasma of active males was associated with spermiogenesis and spermiation events. These findings have not been previously observed in Amazonian freshwater stingrays and demonstrate that the reproductive activity of P. wallacei males is concomitant to the period of rising waters in the middle Rio Negro basin, and is regulated by the action of gonadal steroids, mainly testosterone.

The nurse shark, Ginglymostoma cirratum (Bonnaterre, 1778) is one of the most studied species of elasmobranchs. However, the knowledge of their reproductive biology is still relatively rare, particularly in the western South Atlantic. This study aimed to describe the morphology of the uterus and the ovary of G. cirratum, based on specimens caught off at the Fortaleza/CE coast, northeast Brazil. Samples were collected from September 2012 to June 2013, from regular landings of artisanal fishing, which commercialize this species freely. A total of ten females were collected. The methodologies followed for analyzing the ovaries and uterus of those females included both macroscopic and histological analysis. G. cirratum has internal type ovary morphology, with invaginations of connective tissue, which defines compartments and separate oocyte groups in ovigerous lots. The epithelium lining the ovary changes from simple columnar ciliated in the area without ovigerous lots, which turns into a simple cubic epithelium in the coating portion of the epigonal organ where ovarian tissue is absent. The uterine mucosa has secretory cells denoted by Alcian Blue staining, indicating the production of mucopolysaccharides, even in immature individuals. This lecithotrophic shark has a uterine vascularized mucosa that is one characteristic of viviparous elasmobranch species. RESUMO: O tubarão-lixa, Ginglymostoma cirratum (Bonnaterre, 1778) é uma das espécies mais estudadas de elasmobrânquios. O conhecimento de sua biologia reprodutiva, no entanto, ainda é relativamente raro, particularmente no Oeste do Atlântico Sul. Este estudo objetivou a descrição morfológica do útero e ovário de G. cirratum, baseado em espécimes capturados na costa de Fortaleza/CE, no Nordeste do Brasil. Um total de dez fêmeas foi coletado de setembro de 2012 a junho de 2013, nos desembarques regulares da pesca artesanal, que comercializam essa espécie livremente. A metodologia foi de acordo com as analises macroscópica e histológica dos ovários e útero. G. cirratum tem o tipo de morfologia de ovário interno, com invaginações de tecido conjuntivo, que define compartimentos e separa grupos de oócitos em lotes ovígeros. O epitélio que reveste o ovário varia de epitélio simples colunar ciliado na área que não apresenta lotes ovígeros para epitélio simples cúbico na porção de revestimento do órgão epigonal, onde o tecido ovariano é ausente. A mucosa uterina possui células secretoras, evidenciadas pela coloração em Alcian Blue, indicando a produção de mucopolissacarídeos, mesmo em indivíduos imaturos. Este tubarão lecitotrófico apresenta a mucosa uterina vascularizada, sendo esta uma característica de espécies de elasmobrânquios vivíparos.

This paper reports on a subadult male specimen of the smooth dogfish, Mustelus schimitti, caught in the continental shelf of Rio Grande Sul, during winter of 1993, which exhibited the characteristics of total albinism.Este trabalho registra a primeira ocorrência de albinismo total no cação Mustelus schimitti, capturado, no inverno de 1993, na plataforma continental do Rio Grande do Sul.

The relationship between the distribution of the lateral line canals and their functionality has not been well examined in elasmobranchs, especially among Neotropical freshwater stingrays of the family Potamotrygonidae. The spatial distribution of the canals and their tubules and the quantification of the neuromasts were analyzed in preserved specimens of Potamotrygon motoro, P. orbignyi, Potamotrygon sp. "cururu", and Paratrygon aiereba from the middle Negro River, Amazonas, Brazil. The hyomandibular, infraorbital, posterior lateral line, mandibular, nasal and supraorbital canals were characterized and their pores and neuromasts quantified. The ventral canals are known to facilitate the accurate localization of prey items under the body, and our results indicate that the dorsal canals may be employed in identifying the presence of predators or potential prey positioned above the stingray's body. The presence of non-pored canals in the ventral region may be compensated by the high concentration of neuromasts found in the same area, which possibly allow the accurate detection of mechanical stimuli. The concentration of non-pored canals near the mouth indicates their importance in locating and capturing prey buried in the bottom substrate, possibly aided by the presence of vesicles of Savi. A relação entre a distribuição dos canais da linha lateral e a sua funcionalidade é pouco conhecida para os elasmobrânquios, especialmente para as raias neotropicais da família Potamotrygonidae. A distribuição espacial dos canais e seus túbulos e a quantificação dos neuromastos foram analisadas em exemplares preservados das raias Potamotrygon motoro, P. orbignyi, Potamotrygon sp. "cururu" e Paratrygon aiereba, provenientes do médio rio Negro, Amazonas, Brasil. Foram identificados os canais hiomandibular, infra-orbital, linha lateral posterior, mandibular, nasal e supra-orbital, e os poros e neuromastos de cada um foram quantificados. Nossos resultados mostram que os canais dorsais podem ter a função de identificar a presença de predadores ou presas posicionadas acima do corpo da raia, enquanto os canais ventrais provavelmente permitem uma localização precisa da posição de presas sob o corpo. A existência de canais sem poros na região ventral pode estar relacionada com a alta concentração de neuromastos, que compensaria a falta de contato direto dos neuromastos com o meio externo na detecção de estímulos mecânicos. A concentração dos canais sem poros na proximidade da boca indica sua importância para a localização e captura de presas enterradas no substrato, possivelmente auxiliadas pela presença das vesículas de Savi.

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.

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. 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.