Secondary sexual dimorphism and ontogenetic shifts in habitat use by the lesser guitarfish Zapteryx brevirostris.

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.

Age structure and multi-model growth estimation of longnose stingray Hypanus guttatus (Dasyatidae: Myliobatoidei) from north-east Brazil.

We collected 729 Hypanus guttatus from the northern coast of the state of Rio Grande do Norte (RN), of which 196 were used to estimate age and growth. Ninety-five were male (12.7 to 57.0 cm disc width; WD ) and 101 were female (13.0 to 88.5 cm WD ); females were significantly larger than males. Cross sections of vertebrae showed band-pairs ranging from 0 to > 14 in females and from 0 to 9 in males. New-borns presented an opaque edge at birth in vertebrae without a birthmark. The average percentage of error (APE; %E) for the entire sample provided evidence that ages were repeatable. The mean monthly marginal increment (IM ) indicates annual band-pair formation from August to November. The annual cycle model for one band-pair deposition provided the best fit to data based on the AIC, with peaks between August and October, similar to that found in the IM analysis, suggesting an annual formation pattern. A multi-model approach that included four models based on the observed mean WD at age indicated a modified von Bertalanffy growth model as the best for describing the species growth: W0 (WD at birth) = 14.6 cm for both sexes; females W∞ = 98.61 cm (95% CI = 87.34-114.61 cm); k = 0.112 year-1 (CI = 0.086-0.148 year-1 ); males W∞ = 60.22 cm (CI = 55.66-65.35 cm); k = 0.219 year-1 (CI = 0.185-0.276 year-1 ). The age-at-maturity in males and females is 5 years and 7 years, respectively. The age composition shows that most (84%) specimens were aged 0 to 2 years. The information provided here is essential for analytical assessments of H. guttatus, which is subject to significant fishing pressure mainly on new-borns and juveniles.

Closely Related Fishes Inhabiting Different Ecosystems Exhibit the Same Oocyte Production and Recruitment Pattern.

Information on oocyte production and recruitment in phylogenetically related species can help in understanding the evolution of reproductive life-history traits in fish of indeterminate fecundity. The present study compared, for the first time, oocyte production and recruitment patterns between two closely related species: Stellifer brasiliensis and Stellifer rastrifer (Perciformes, Sciaenidae), in the southwestern Atlantic, Brazil. Specimens of S. brasiliensis were sampled from the coastal waters of Ubatuba, and samples of S. rastrifer were taken from the Cananéia Lagoon Estuarine System. Ovaries were investigated using histology and model-based stereology. The total number of oocytes per individual (N) and stage-specific oocyte packing density did not differ significantly between S. brasiliensis and S. rastrifer The number of pre-vitellogenic and vitellogenic oocytes were positively correlated with female total weight and length, and ovary weight in both species. Analysis of oocyte recruitment across their development stages revealed that approximately 5.9% of the standing stock oocytes larger than 50 µm in S. brasiliensis and 5.0% in S. rastrifer were recruited to form the next batches. Females of S. brasiliensis and S. rastrifer, in spawning-capable phase, exhibit the same oocyte production and recruitment patterns, showing no influences of the ecosystems on primary and secondary oocyte production.