Length at Maturity, Sex Ratio, and Proportions of Maturity of the Giant Electric Ray, Narcine entemedor, in Its Septentrional Distribution

The size at which a certain fraction of a fish population reaches sexual maturity is an important parameter of life history. The estimation of this parameter based on logistic or sigmoid models could provide different ogives and values of length at maturity, which must be analyzed and considered as a basic feature of biological reproduction for the species. A total of 305 individuals of Narcine entemedor (N. entemedor) were obtained from artisanal fisheries in the Bahía de La Paz, Mexico. For the organisms sampled, sexes were determined and total length (TL) in cm was measured from October 2013 to December 2015. The results indicated that the females were larger, ranging from 48.5 cm to 84 cm TL, while males varied from 41.5 cm to 58.5 cm TL. The sex ratio was dominated by males ranging from 45–55 cm TL, while females were more abundant from 60 to 85 cm TL. Mature females were present all year long, exhibiting a continuous annual reproductive cycle. The length at maturity data were described by the Gompertz model with value of 55.87 cm TL. The comparison between models, and the model selection between them, showed that the Gompertz model had maximum likelihood and smaller Akaike information criterion, indicating that this model was a better fit to the maturity proportion data of N. entemedor.

Husbandry and captive reproduction of the giant Mexican leaf frog Agalychnis dacnicolor

The giant Mexican leaf frog, Agalychnis dacnicolor, is a large arboreal frog endemic to Mexico. This species was previously under-represented in European zoological collections and specific techniques for reproductive management under vivarium conditions little known. A group of four males and one female A. dacnicolor were maintained in captivity at Chester Zoo (Great Britain). To bring them into reproductive condition, they were subjected to three simulated environmental phases that differed in temperature, humidity and feeding regime. This proved successful so that two clutches of spawn, each containing 150-300 eggs, were deposited on leaves overhanging water. Tadpoles hatched from 4 days following oviposition with approximately 80 % success rate. They were reared at a water temperature of 27 °C to 29 °C and displayed no negative effects from living in high density. All tadpoles metamorphosed successfully and froglets with resorbing tails left water after about 32 days. Their tails were resorbed in a further 4 to 5 days at which time they began to feed; at least in the case of males, sexual maturity was reached after 10 months. This methodology will enable zoological collections in Europe to breed this species for potential conservation, research and educational purposes.

Just metamorphosed amphibians: imagos or metamorphs?

The term metamorph for just metamorphosed amphibians appeared surreptitiously in the batrachological literature. It is shown here that this term is linguistically unjustified and conceptually confusing, as it has never been associated with a clear, formal definition stating in particular when does this developmental stage start and end. The use of the term imago for an individual resulting from the last metamorphosis following a larval stage, which exists for insects since 1767 and for amphibians since 1808, is much preferable. For amphibians, the formal definition of this term was given in 1978 as an animal having completed its metamorphosis, before having substantially grown and until the first major ecological event in its life cycle (such as migration, hibernation or aestivation). In amphibians, this stage is followed by a stage juvenile and a stage subadult until the stage adult is reached, which is defined by sexual maturity and ability to reproduce. Given the diversity of developmental modes in the animal kingdom, it would be vain to try to homogenise the terminology of all detailed developmental stages across all groups. However, the possibility to homogenise the use of the term imago throughout zoology for specimens resulting from the ‘last metamorphosis’ (i.e., drastic change not only of form but also in some anatomical structures), whether followed by growth and minor transformations or not, and whether associated with sexual maturity or not, would certainly be worth considering. This would allow to have a few general descriptive terms to designate the main similar, but not homologous, ‘landmarks’ observed in the development of many animals (egg, larva, imago and adult), just like we have a general term (metamorphosis) for ‘similar’ phenomena which are not homologous. This would not prevent specialists of the various zoological groups to have specific terms for more precisely defined ‘stages’ which are proper to these groups.

Effects of Degradation of Nonylphenol in Waste Water by Strong Ionization and Its Degradation Products on Sex Differentiation in Zebrafish

Nonylphenol (NP), as a typical environmental endocrine disruptor, exists widely in the natural environment. It has a high toxicity with a low concentration. NP at the level of μg/L is enough to interfere with the sex differentiation of many aquatic organisms. The effects of degradation of NP in waste water by strong ionization (SID) and its degradation products on sex differentiation in zebrafish was studied in this paper. The NP solution of 5mg/L was degraded by SID device, and the 20d zebrafish were exposed to NP wastewater of different concentrations before and after degradation until their sexual maturity. The body length, body weight and sex differentiation ratio of zebrafish were recorded, and the sex hormone levels of zebrafish were extracted and detected. The gonadal glands of zebrafish were slices and analysed. This study found that the effects of nonylphenol on male zebrafish were much greater than that of female, and there was no significant positive correlation between toxicity and dose. In addition, the effects of 5mg/L NP wastewater degraded by SID for 60min were not significantly different from those of the control group, indicating that SID could effectively degrade NP and alleviate its biological toxicity.