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BACKGROUND: Mobulidae is a monophyletic family within the Myliobatiformes that comprises pelagic species represented by manta and devil rays. Among the genus Mobula, the Atlantic Pygmy Devil Ray - Mobula hypostoma - is reported in coastal regions exclusively in tropical and subtropical Atlantic Ocean from 1 to 100 m deep. In Brazil, M. hypostoma is one of the least studied Mobula species. It is regularly misidentified, especially as Mobula thurstoni, and is commonly listed as bycatch, in fishery inventories, or related to opportunistic sightings in the national territory. METHODS AND RESULTS: Here, we describe the complete nucleotide sequence of the mitochondrial genome (mitogenome) from Mobula hypostoma, which is 18,141 bp in length and comprises 13 protein-coding, two ribosomal RNA, and 22 transfer RNA genes. The M. hypostoma mitochondrial genes organisation and mitochondrial genome length are similar to other Mobula species, and the phylogenetic reconstruction indicates M. hypostoma as closely related to Mobula munkiana. CONCLUSIONS: The Brazilian mitogenome of M. hypostoma is expected to be a valuable resource for molecular-based species identification, and evolutionary and phylogeography studies.

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Neotropical freshwater stingrays of the subfamily Potamotrygoninae exhibit aplacental viviparity with uterine trophonemata. In this reproductive mode, females nourish and provide oxygenation to the embryo via the mucosa of the uterine wall. The aim of this study was to describe and histologically quantify the tissue components of the gravid uterus in an Amazonian freshwater stingray. Adult females of Potamotrygon wallacei were studied in different reproductive periods: resting stage, pregnant, and postpartum. During reproductive rest, the left ovary has numerous follicles compared to the right side. Therefore, uterine fertility is usually higher on the left side. The presence of an embryo in the right uterus suggests that the right ovary is also functional, although this only occurs in larger females. In females at reproductive rest, the wall of the uterus is formed by a mucosal layer (without the trophonemata) that contributes 16.7% to the thickness, while the myometrium accounts for 83.3% of the thickness. The mass-specific volume of the mucosal layer, inner circular, and outer longitudinal smooth muscle sheets tend to increase in the gravid uterus, indicating hypertrophy and hyperplasia of these components. During pregnancy, the trophonemata undergo marked tissue remodeling. Epithelial cells are organized into glandular acini and have apical secretory vesicles; furthermore, peripheral blood vessels proliferate and become dilated. These characteristics demonstrate that the gravid uterus of P. wallacei presents intense uterolactation activity and provides oxygenation to the fetus. Tissue remodeling occurs only in the uterus with the presence of an embryo. During postpartum, females have low body condition factor indicating a high reproductive cost. This study contributes to the knowledge of the reproductive biology of this species and will help us understand the impacts of climate change on the breeding areas of potamotrygonids.

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Maternal offloading of polycyclic aromatic hydrocarbons (PAHs) poses a significant exposure route for developing embryos, with implications for subsequent generations. Despite known developmental effects regarding fish physiology and behavior, maternal PAH transfer assessments in elasmobranchii are still lacking. This study investigated PAH contamination and maternal transfer in one female Lesser Numbfish (Narcine brasiliensis) electric ray and seven embryos for the first time. Naphthalene was identified as the predominant low molecular weight PAH, and dibenzo[a,h]anthracene was the most abundant high molecular weight compound. Most embryos exhibited some level of PAH exposure, with varying accumulation patterns potentially influenced by size, developmental stage, and yolk absorption rates. Further investigation is warranted to understand the impacts of PAH maternal offloading on elasmobranchii uterine contents and embryos.

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This work aimed to describe and quantify the tissue components of the digestive tube of the neotropical freshwater stingray, Potamotrygon wallacei. For this, conventional histology and stereological methods were used to estimate tissue volume. The volumes of the four fundamental layers and the tissue components in the stomach (cardiac and pyloric) and spiral intestine were also estimated. In the cardiac stomach, the mucosa layer occupies 44.7% of the total volume of the organ wall. The gastric glands are the main components, and these structures alone represent 49.7% of this layer. This large number of gastric glands suggests a high potential for processing food items with a high protein content. The stereological methods were sensitive enough to show a reduction in the volume of the gastric glands from the cardiac region toward the pyloric region. Gastric glands are absent in the pyloric region of the stomach. However, the muscularis becomes thicker towards the pyloric region. The increase in smooth muscle thickness is due to the thickening of the inner muscular layer. This suggests that the role of the pyloric stomach may be related to the mixing of the chyme and assisting its passage to the spiral intestine. In the spiral intestine, data on the volume of the mucosa layer (and epithelial lining) suggest that the spiral valve has a large absorptive area. In several respects, the morphology of the digestive tube of P. wallacei is similar to that of other batoids. However, its slight morphological variations may be related to the habitat specificity of this species.

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The genus Urotrygon comprises small- to medium-sized endemic round rays on the American continent and has undergone several synonymization processes. Here, we used an integrative taxonomic approach, including meristic, morphometric, and mtDNA analyses, to resolve the particularly intricate relationship among Urotrygon munda Gill, 1863, Urotrygon chilensis (Günther, 1872), and Urotrygon asterias (Jordan & Gilbert, 1883). The latter species is currently a synonym of U. munda but is also considered the U. chilensis "northern morphotype." These taxonomic entities have historically been confounded, mainly due to their phenotypical resemblance along their geographic distribution in the eastern Pacific. We assessed 78 specimens (43 "northern" and 30 "southern morphotypes" of U. chilensis, as well as 5 U. munda) using 19 external variables for taxonomic and morphometric analysis. Distinct meristic patterns, including pectoral and pelvic ceratotrichia, vertebrae number, and thorn distribution along the dorsal midline, were observed in the series-type specimens of the three taxonomic entities. Our multivariate morphometric analyses consistently differentiated the three groups as distinct taxonomic entities, with an overall classification accuracy of 66.7%. The meristic results also provided reliable information distinguishing the three entities. Based on the nicotinamide adenine dinucleotide (NADH2) and cytochrome oxidase subunit I (COI) genes, our phylogenetic analysis were consistent with the morphometric and meristic data, supporting these three entities as distinct species having their own evolutionary lineages. Our comprehensive approach confidently demonstrated that the northern U. chilensis morphotype matched and corresponded to the description of the Starry round ray, U. asterias, confirming its taxonomic resurrection as a valid species distinct from U. chilensis and U. munda. The geographic distribution of U. asterias spans from the tropical west coast of Mexico (including the Gulf of California) to Costa Rica, revealing that microevolutionary processes have well-defined population clades within this range. Furthermore, U. chilensis is unequivocally established as the sole Urotrygon species occurring south of the Guayaquil marine ecoregion. In addition, the public COI and NADH2 sequences available for Urotrygon hosted in the ad hoc online databases were found to be misidentified, emphasizing the need for rigorous taxonomic scrutiny in this group. Finally, our research underscores the significance of an integrative approach that combines morphometric, meristic, and molecular techniques with historical data to disentangle the complexities of closely related taxa.

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The Rio de Janeiro Marine Aquarium (AquaRio) is the first to successfully maintain and reproduce the spiny butterfly ray (Gymnura altavela), providing unique information about the species' biology. Seven rays were kept in captivity between 2018 and 2023, two captured on the southeastern coast of Brazil and five born in the aquarium. The applied abiotic conditions and nutrition allowed for the survival, growth, and reproduction of these individuals. Growth parameters (asymptotic disk width-DW∞ and growth coefficient-k) were estimated based on the von Bertalanffy model using the Fabens method for males and females separately. The best models estimated DW∞ = 106.47 cm and k = 0.396 for males and DW∞ = 172.2 cm and k = 0.190 for females. Sexual dimorphism was corroborated, with females reaching larger sizes and presenting slower growth rates than males. The estimated k values were higher than those estimated for rays of similar size to G. altavela in the natural environment, probably due to the constant water temperature (around 25.5°C), food abundance, low population density, reduced predation rates, and high water quality in the captive environment. A comparison of the captivity findings with other studies on G. altavela age and growth in the Atlantic and Mediterranean indicates a broad phenotypic plasticity regarding growth. Three G. altavela reproductions were recorded, with size at birth appearing to be a key factor for pup's survival. Behavioral pattern observations associated with reproduction are also described, encompassing chasing and copulation, whereas the species' internal morphology is described through coelomic cavity ultrasound scanning.

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This paper presents information on the morphological, morphometric, and dental sex differences in the dwarf round ray Urotrygon nana. We recorded 12 morphological traits, sex, the distribution pattern of dermal denticles, the number of tooth rows, and the tooth shape of 466 individuals. The disc width of females ranged from 50 to 172 mm and that of males ranged from 53 to 135 mm. A neuronal classification model and a correspondence analysis showed that female disc width was 21.5% broader, and the distance from the rostrum to the anus was 17.7% longer than that of males, whereas males presented 19.5% greater distance between the nostrils, 9.7% greater preorbital snout length, 6.8% greater cloaca to caudal-fin length, 2.7% greater interorbital distance, and 1.1% greater total length than females. The disc of adult males, including the abdominal cavity area, was densely covered with dermal denticles, which were slightly larger than those observed in females. Females presented homodont dentition with molariform teeth and a smooth lozenge-shaped crown with rounded margins. Males exhibited homodonty but with tooth morphology variations in individuals of different sizes (from molariforms to sharper cusp teeth). There were changes in disc shape (from subcircular to oval), distribution and size of dermal denticles (more abundant and larger), and tooth shape (from molariform to monocuspid teeth) during male development, from neonates to adults. U. nana exhibited sexual dimorphism in size, disc shape, number and shape of teeth, and distribution and size of dermal denticles.

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From December 2012 to June 2014, 796 Pacific guitarfish were caught in 183 fishing sets in northern Peru. Catch occurred in 86.3% of sets. Most individuals caught were mature with a bias toward males. The mean total length for females and males was 83.4 cm, and 91.1 cm, respectively. The capture per unit effort (CPUE) was 12.6 ± 3.4 guitarfish (km.12 h)-1. The length-weight relationships showed that this species presents a sexual dimorphism in growth. These results support the importance of Sechura Bay as a key area for this species. This study represents the first species-specific fishery data for the Pacific guitarfish.

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Sexual dimorphisms are generated by divergent processes, such as natural or sexual selection and niche convergence. Males and females of the lesser guitarfish, Zapteryx brevirostris, present morphological differences in their discs, and the relationships with the species biology and ecology were unrecognized. Analysing the morphometry of 201 specimens and the influence of bottom features on the frequencies of 188 specimens among life stages and sexes, we found strong evidence that gonadal maturation leads to dimorphisms on discs, validating a concavity on male pectoral fins as a secondary sexual dimorphism and rejecting the hypothesis that such dimorphisms were related to ecological pressures. The principal component analysis (PCA) and permutational MANOVA (PERMANOVA) analyses revealed that males and females shared similar body aspects until they reached maturity, mainly due to lower variations in WD, WR, LD, DPRO, and LSC at younger life stages. The relationships of these variables with LT corroborate the former results, showing a changing point around LT > 30 cm where females started to attain larger measurements than males. Moreover, we revealed ontogenetic shifts, with adults from both sexes exploring different habitats than juveniles and subadults. Differences in frequencies of each life stage were best explained by organic matter (OM) with the adults exploring bottom habitats of higher concentrations of OM than juveniles and subadults, strengthening the assumption that body differences between sexes are not related to ecological pressures. These results bring not only new insights about the possible advantages that those morphometric differences provide to males while mating but also information about the abiotic influences on species distribution, which, along with knowledge of local oceanographic dynamics and benthic community patterns, would inform actions for species conservation.

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Elasmobranchs are good indicators of marine pollution as they accumulate pollutants from water and food, and occupy different trophic levels. Concentrations of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs) and chlorpyrifos were quantified in muscle, liver, gonads, gills, and brain in both sexes and maturity stages of the Southern Eagle Ray, Myliobatis goodei, captured in Argentine coastal waters. Moreover, possible histological alterations in the liver and gonads were analyzed. Pollutant concentrations were pervasive across all tissues, with PCBs > OCPs > chlorpyrifos. Elevated pollutant levels were notably found in the liver and gills. We identified thirty-six PCB congeners in tissues, with low-chlorine congeners prevailing. Among OCPs, ∑DDT and ∑endosulfan were predominant. Females exhibited higher pollutant levels in most tissues compared to males, except in the gonads, and adults generally displayed elevated pollutant levels. Histological analysis revealed the presence of atretic follicles and melanomacrophages (MM). Continuous monitoring of pollutant levels, alongside their effects on physiological and ecological traits, is imperative for effective management and conservation efforts.

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Interspecific interactions, including predator-prey, intraguild predation (IGP) and competition, may drive distribution and habitat use of predator communities. However, elucidating the relative importance of these interactions in shaping predator distributions is challenging, especially in marine communities comprising highly mobile species. We used individual-based models (IBMs) to predict the habitat distributions of apex predators, intraguild (IG) prey and prey. We then used passive acoustic telemetry to test these predictions in a subtropical marine predator community consisting of eight elasmobranch (i.e. shark and ray) species in Bimini, The Bahamas. IBMs predicted that prey and IG prey will preferentially select habitats based on safety over resources (food), with stronger selection for safe habitat by smaller prey. Elasmobranch space-use patterns matched these predictions. Species with predator-prey and asymmetrical IGP (between apex and small mesopredators) interactions showed the clearest spatial separation, followed by asymmetrical IGP among apex and large mesopredators. Competitors showed greater spatial overlap although with finer-scale differences in microhabitat use. Our study suggests space-use patterns in elasmobranchs are at least partially driven by interspecific interactions, with stronger spatial separation occurring where interactions include predator-prey relationships or IGP.

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The elucidation of energetic patterns in adult viviparous elasmobranchs and their offspring can contribute to understanding ecophysiological questions, such as maternal-fetal metabolism and group life-history traits. We characterized the energetic substrates in pregnant individuals and stages of offspring development in the freshwater stingray Potamotrygon amandae. Our results show that the energetic distribution of the yolk is composed of more lipids than proteins, whereas the inverse pattern is observed in the egg and uterus, proving the plasticity of the energy provision of the species. As a novelty, we describe that yolk/intestine transfer occurs in this species.

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This paper describes the fishing profile and the temporal variation in the commercial landings of elasmobranchs in a global hotspot for their conservation and investigates the variables that influenced the landings. Census data on commercial catches were obtained between April 2008 and October 2010 from nine landing sites in Bragança (Pará, northern Brazil). Five vessel types, four fishing gears, and eight fishing techniques engaged with elasmobranch capture were identified. A total of 2,357 landings were recorded, with a total production of 354 t. The highest yields were recorded in 2009, with sharks being harvested mostly by small and medium-sized vessels, and batoids, by small vessels and canoes. Drifting nets and longlines played a prominent role in elasmobranch fisheries. The results show that the landings were influenced by days at sea, which is common in tropical fisheries. The elasmobranch data series is discontinuous as statistics are absent for most fishing sites albeit imperative for proper management, as well as relevant for decision-makers focusing on their conservation.

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The evaluation of hematological and plasma biochemical parameters and the subsequent establishment of reference intervals facilitate the diagnosis of the health status of animals. This work aimed to determine the blood parameters of wild specimens of the stingrays Potamotrygon motoro and Potamotrygon orbignyi from the lower Solimões River region, Amazonas, Brazil. One hundred forty-one stingrays were captured, 92 specimens of P. motoro and 49 of P. orbignyi, of both sexes and at different stages of development. No effect of sex was observed on the blood parameters of juvenile animals for both species. P. motoro neonates presented a distinct hematological and biochemical profile, with significantly lower hematocrit values, hemoglobina, number of erythrocytes, mean corpuscular hemoglobin concentration, monocytes, plasma glucose, total proteins, albumin, and globulin. On the other hand, total cholesterol and urea levels were significantly higher in this same group compared to juveniles of the same species. Comparison between species revealed lower values of triglycerides and total cholesterol in P. orbignyi of both sexes. The results obtained are pioneering for these Amazonian species in white water environments and will serve as a basis for evaluating the health status of wild stingrays. Thus, from the analysis of the blood of the P. motoro and P. orbignyi stingrays, it was possible to observe good health conditions.

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An adult female Brazilian cownose ray (Rhinoptera brasiliensis), housed in Ubatuba Aquarium died after loss of appetite period. During necropsy, an enterolith was discovered partially obstructing the intestinal lumen. Examination of the enterolith revealed a bonefish spine nidus. Enterolithiasis has been linked to multiple factors including diet, genetics, alkaline intestinal environments and, as in this particular case, the ingestion and retention of foreign bodies. The composition of this enterolith from a cownose ray was primarily monohydrocalcite. This short communication, apparently the first to report enterolithiasis in stingrays, emphasizes the need for post-mortem examinations of carcasses on macroscopic and microscopic levels.

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The short-tail yellownose skate, Zearaja brevicaudata, occurs off southern Brazil and along the Argentine continental shelf, including waters surrounding the Islas Malvinas and the upper slope, and is very frequently caught by trawl fisheries throughout its range. The age, growth, and maturity of Z. brevicaudata were investigated using 204 individuals collected by commercial fishing vessels from northern Argentina, between March 2016 and September 2019. Age was determined on a sample comprising vertebrae from 151 individuals, 60 males, ranging in size from 391 to 956 mm total length (TL), and 91 females, ranging in size from 324 to 1060 mm TL. Maximum ages determined for males and females were 22 and 29 years, respectively. A Bayesian framework was employed with a set of three candidate models to estimate growth parameters (von Bertalanffy, Gompertz, and Logistic). The von Bertalanffy model had the best fit, and the sexes showed undistinguishable growth parameters. For sexes combined, derived growth mean parameters (± S.D.) were L∞ = 1081 mm ± 64.34 mm, k = 0.09 ± 0.01 years-1, and L0 = 248 mm ± 23.52 mm. The age at maturity was estimated at 13.15 and 14.66 years for males and females, respectively.

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Round rays (family: Urotrygonidae) are commonly caught as by-catch by shrimp trawl fisheries in the tropical eastern Pacific (TEP). However, little information on their life history and catch species composition exists for most round ray species, preventing the evaluation of the impact of fishing on their populations. The mean size at sexual maturity (DW50), seasonal variation by maturity stages, and fecundity for two round ray species caught during shrimp trawl research cruises in the south-eastern Gulf of California (northern TEP) were estimated using a multi-model approach and inference for the first time, to determine the part of the population of each species that is being affected by shrimp trawling. Disc width (DW) ranged from 7.0 to 30.9 cm for the spotted round ray (Urobatis maculatus), and 7.2-33.5 cm for the thorny stingray (Urotrygon rogersi), with females reaching larger sizes than males in both species. The DW50 was estimated at 12.8 and 11.8 cm DW for the males and females of U. maculatus, respectively, whereas for U.rogersi, it was 15.0 and 18.4 cm DW for males and females, respectively. Embryos were found in females ≥14.5 cm DW in both species. The maximum fecundity was five embryos for U. maculatus (mean = 3.1 ± 0.2 S.E., mode = 4), and six embryos for U. rogersi (mean = 3.0 ± 0.3 S.E., mode = 2). Fecundity and embryo size did not vary with maternal size. Male and female immature and mature individuals for both species, including pregnant females, were found in the catches in all seasons of the year. Our results can help determine the vulnerability of the studied species populations to fishing pressure from shrimp trawling in the northern TEP and guide the development of future monitoring strategies and conservation actions for these species, if necessary.

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Knowledge of thermal tolerance limits provides important clues to the capacity of a species to withstand acute and chronic thermal changes. Climate models predict the increase and intensification of events such as heat waves, therefore understanding the upper thermal limits that a species can tolerate has become of utmost importance. We measured the upper thermal tolerance of the endemic Magdalena river stingray Potamotrygon magdalenae acclimated to experimental conditions, and then used critical thermal methodology to find the temperature at which an organism reaches a critical endpoint where locomotory activity becomes disorganized and the animal loses its ability to escape from conditions that will promptly lead to its death. We also describe the behavioral response of individuals to acute thermal stress and infer the possible consequences of temperature increases in the habitats of P. magdalenae populations. There were no significant differences between sexes in temperature tolerance or behavior. The critical thermal maximum (39°C) was 5.9°C above the maximum recorded temperature for the study area. Although P. magdalenae was tolerant to high temperature and currently is not living at its upper thermal limit, its survival in Guarinocito Pond will be threatened if temperatures continue to increase, considering the warming scenarios predicted for tropical regions due to climate change, even including short-term climate phenomena such as El Niño.

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Abstract This research aimed to estimate the length-weight ratio (LWR) of the stingray Potamotrygon wallacei, known locally as the cururu, which was caught in streams and lakes in the middle Negro River region, Amazonas, Brazil. The stingrays were captured during the night (from 11 pm to 1 am) near the shores of streams and lakes, through active search using wooden canoes, head lanterns and scoop nets. The samplings were carried out in November 2017 (5 days), February (8 days), March (3 days) and April (2 days) of 2018, totaling 18 days of sampling. The total fresh weight was measured to 0.1 g of accuracy and the disc width to 0.1 cm accuracy. The parameters a and b of the equation W=a.DWb were estimated. This study provides new maximum length data for the cururu stingray.

Resumo Esta pesquisa teve como objetivo estimar a relação peso-comprimento (LWR) da arraia Potamotrygon wallacei, conhecida localmente como cururu, que foi capturada em igarapés e lagos na região do médio Rio Negro, Amazonas, Brasil. As arraias foram capturadas durante a noite (das 23h-1h) nas margens dos igarapés e lagos, por meio de busca ativa utilizando canoas de madeira, lanternas de cabeça e puçás. As coletas foram realizadas nos meses de novembro de 2017 (5 dias), fevereiro (8 dias), março (3 dias) e abril (2 dias) de 2018, totalizando 18 dias de amostragem. Foram medidos o peso fresco total com precisão de 0,01 g e a largura do disco com precisão de 0,1 cm. Os parâmetros a e b da equação W= a.DWb foram estimados. Este estudo prover novos dados de comprimento máximo para a arraia cururu.

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Mercury is an element with potential risk to fish and those who consume it. Thus, this study aimed to determine the levels of total mercury (THg), carry out a health risk assessment related to the consumption of the freshwater stingrays Potamotrygon motoro, and determine the physical and chemical properties of the water where stingrays occur. Stingrays of the species P. motoro were obtained from the Amazon River, and samples of the animals' musculature were collected to determine THg levels. Risk assessment was conducted using pre-established formulas of estimated monthly intake (EMI), maximum monthly intake rate (IRmm), and hazard quotient (HQ). Three population scenarios were evaluated, considering both sexes and differences between rural and urban areas. There was no relationship between weight and THg concentration nor between total length and THg concentration. Higher EMI values were observed in rural children; for the IRmm, male children had the lowest consumption levels. For the hazard quotient, there was a similarity between the three age groups when comparing the male and female sexes. In addition, the representatives of the rural area always had lower values than the urban area. Freshwater stingrays, like other elasmobranchs, can be crucial animal species because they act as sentinels in studies that assess harmful chemicals like mercury.

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