Sexual dimorphism in the dwarf round ray Urotrygon nana.

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.

Spatial pattern of distribution and reproductive strategy of vermiculate electric-rays Narcine vermiculatus.

In the study, the authors evaluate the spatial distribution pattern of vermiculate electric-ray Narcine vermiculatus using geostatistical techniques to predict its spatial distribution and indicate its reproduction strategy. From January 2008 to December 2009, 3333 specimens of vermiculate electric-ray were caught. Total length (LT ), sex, maturity stage, catch location and depth were recorded for each specimen. The LT of vermiculate electric-ray ranged from 6.7-24.6 cm. The authors estimate an irregular spatial structure, with a high-density patch ( x ¯ = 53 ind. ha-1 ) located on the east coast, which concentrates 65.2% of the specimens. The high-density patch consists mainly of large juveniles (13.3-19.5 cm LT ), sub-adults (14.0-19.8 cm LT ) and young adults (14.7-21.3 cm LT ). Data indicate that adults migrate to the high-density patch to reproduce. Males reached maturity at 14.5 cm LT , whereas females reached maturity at 19.3 cm LT . Vitellogenesis in female vermiculate electric-ray begins in June; ovulation, mating, fertilization and gestation in October and birth begins in February. This indicates an annual cycle with vitellogenesis and consecutive gestation, in females synchronized in reproduction. Fecundity was 1-8 ( x ¯ = 4), and the sex ratio of embryos was 1:1. The birth occurred between February and April, with an average size at parturition of 6.3 cm LT . Incidental capture of sub-adults and adults of N. vermiculatus by bottom trawls threatens the survival of this species.

Presence of pregnant females of the Gorgona guitarfish, Pseudobatos prahli, in the Mexican tropical Pacific.

Five specimens (four females and one male) of the Gorgona guitarfish, Pseudobatos prahli, were sighted during two dives carried out off the western Gulf of Tehuantepec. This document describes the reproductive condition of three adult females captured, two of which had uterine eggs, whereas one had embryos. The sighting and capture of specimens occurred during two Tehuano wind events; the authors, therefore, believe that variations in temperature and dissolved oxygen could have affected P. prahli, leading it to carry out temporal migrations towards coastal shallow waters.