Variación Morfológica en la Musculatura Cefálica de Diplobatis ommata y Narcine vermiculatus (Chondrychthyes: Narcinidae) / Morphological Variation in the Cephalic Musculature of Diplobatis ommata and Narcine vermiculatus (Chondrychthyes: Narcinidae)

Los trabajos realizados sobre batoideos han demostrado que existen grandes variaciones en la musculatura de la región cefálica ventral, estos cambios están asociados a los diferentes estilos de vida de los organismos y por tanto, a los mecanismos de alimentación. El objetivo de este trabajo fue llevar a cabo un estudio comparativo de la morfología de la musculatura cefálica dorsal y ventral de dos especies de la familia Narcinidae: Narcine vermiculatus y Diplobatis ommata. Se observó que ambas especies comparten un patrón morfológico común. Los músculos que mostraron mayores variaciones en la región dorsal fueron el depresor rostral, el preorbital lateral y el elevador rostral. La diferencia más importante en esta región, entre ambas especies, fue la ausencia del músculo cucularis en D. ommata. En la región ventral las principales diferencias se observaron en los músculos depresor mandibular, preorbital medial, interbranquial y depresor hiomandibular. Este último músculo está formado por dos paquetes en D. ommata, en tanto que en N. vermiculatus por uno. Se puede concluir que la morfología de la musculatura cefálica es constante; sin embargo, se observan diferencias importantes en el grado de desarrollo de los músculos tanto en la región dorsal como en la ventral.

SUMMARY: Works conducted on batoids have revealed large variations in the musculature of the ventral cephalic region, associated to the different lifestyles of these organisms and, therefore, to their feeding mechanisms. This work aimed to conduct a comparative study of the dorsal and ventral cephalic muscular morphology of two species of the family Narcinidae: Narcine vermiculatus and Diplobatis ommata. It was observed that both species share a common morphological pattern. Muscles with larger variations in the dorsal region were the rostral depressor, the lateral preorbital and the rostral elevator. The most relevant difference in this region between both species was the absence of the cucularis muscle in D. ommata. In the ventral region, the main differences were observed in the mandibular depressor, medial preorbital, interbranchial and hyomandibular depressor muscles. In D. ommata, the latter is formed by two packages, and by one in N. vermiculatus. It can be concluded that the cephalic musculature is constant; however, significant differences are observed in the muscle development degree in both the dorsal and the ventral regions.

Growth and derived life-history characteristics of the Brazilian electric ray Narcine brasiliensis.

The majority of batoids are listed as Threatened (20.4%) or Data Deficient (41%) by the IUCN Red List. A key challenge to assessing Data-Deficient species is obtaining estimates of key life-history characteristics. Here, a Bayesian approach was used to estimate derived life-history characteristics from a growth model applied to the Data-Deficient Brazilian electric ray Narcine brasiliensis. The age of 170 specimens (107 females, 63 males) was estimated from vertebral centra, and total length, disc width, total weight and birth size were used in a joint estimation of sex-specific length-weight models and two-dimensional von Bertalanffy growth models. Estimates of age at length zero, age at maturity, longevity and mortality at age were derived simultaneously. The Bayesian joint modelling approach was robust to small sample sizes by adding a likelihood to constrain L0 and sharing parameters, such as Brody growth coefficient between length measurements. The median growth parameter estimates were a shared L0 = 38.8 mm, female L∞ = 515 mm, 𝑘 = 0.125 and male L∞ = 387 mm, 𝑘 = 0.194. Age at maturity was estimated to be 7.40-7.49 years for females and 4.45-4.47 years for males, whereas longevity was 22.5-22.6 years for females and 14.2 years for males depending on length measurement. Age-1 natural mortality was estimated to be 0.199-0.207 for females and 0.211-0.213 for males. The derived life-history characteristics indicate N. brasiliensis is earlier maturing, but slower growing relative to other Torpediniformes. These characteristics along with the species' endemism to southern Brazil and high by-catch rates indicate that one of the IUCN Red List threatened categories may be more appropriate for the currently Data-Deficient status. The Bayesian approach used for N. brasiliensis can prove useful for utilizing limited age-growth data in other Data-Deficient batoid species to inform necessary life characteristics for conservation and management.

Dentition of the apron ray Discopyge tschudii (Elasmobranchii: Narcinidae).

The present study provides quantitative and qualitative analyses of the dentition of Discopyge tschudii. Overall, 193 individuals (99 males and 94 females) of D. tschudii were collected on scientific trawl surveys conducted by the National Institute for Fisheries Research and Development (INIDEP) and commercial vessels in Argentina. Discopyge tschudii has rhombic-shaped teeth, arranged in a semipavement-like dentition; each tooth has an erect cusp slightly inclined posteriorly and holaulachorized root. Mature males have greater tooth lengths than females and immature specimens. Discopyge tschudii exhibits dignathic homodonty and gradient monognathic heterodonty where teeth of the commissural row are shorter than those of the symphyseal and internal rows.

Distribution and reproductive biology of the Electric ray Discopyge tschudii Heckel, 1846 in San Matías Gulf, Northern Patagonia, Argentina

The Electric ray Discopyge tschudii is distributed in the Southwest Atlantic from southern Brazil to southern Argentina and in the Southeast Pacific from Peru to southern Chile. The main threat to this species is fishing. Discopyge tschudii is noncommercial and individuals caught are discarded on board. The present study analyzes the distribution and the morphological and reproductive characteristics of this ray in San Matías Gulf (SMG), Argentina. A total of 1087 individuals were analyzed. The species presented an aggregate distribution, with the main concentrations in the northern and eastern areas of SMG, at depths below 100 m. Males ranged from 9 to 43 cm and females from 11 to 38 cm. The species presented sexual dimorphism. Males were larger and heavier than females and also matured at larger sizes. Size at 50 percent of maturity was estimated at 30 cm for males and 21 cm for females. A total of 199 embryos were sampled and the proportion of sexes showed no significant differences from the expected 1:1. The number of embryos per female varied from 1 to 12. The most frequent values were 2 and 5. Length at birth was estimated at 82.17 ± 3.87 mm. Based on our findings, we hypothesize that the electric ray D. tschudii completes its reproductive cycle in SMG.

La raya eléctrica Discopyge tschudii se distribuye, en el Atlántico Sudoccidental, desde el sur de Brasil hasta el sur de Argentina y en el Pacifico Sudoriental desde Perú al sur de Chile. La principal amenaza para la especie es la pesca. Es una especie sin valor comercial y debido a esto los ejemplares capturados por las embarcaciones pesqueras son descartados a bordo. En el presente estudio se analizan la distribución espacial y las características morfológicas y reproductivas de la especie en el Golfo San Matías (GSM), Argentina. Un total de 1087 ejemplares fueron analizados. La especie presentó una distribución agregada, encontrándose las principales concentraciones en el sector norte y este del GSM a profundidades menores a los 100 m. Los machos midieron entre 9 y 43 cm de largo total y las hembras entre 11 y 38 cm. La especie exhibió dimorfismo sexual, siendo los machos más grandes, más pesados y presentando mayores tallas de madurez que las hembras. La talla de madurez a la cual el 50 por ciento de la población alcanzó la madurez sexual fue estimada en 30 cm en machos y 21 cm en hembras. Se analizaron 199 embriones. Las proporciones de sexos de los embriones no mostraron diferencias significativas de lo esperado 1:1. El número de embriones por hembra varió de 1 a 12, siendo los valores más frecuentes 2 y 5. La talla de nacimiento fue estimada en 82,17 ± 3,87 mm. De acuerdo a nuestros resultados se hipotetiza que D. tschudii completa su ciclo reproductivo en el golfo.