The radius of each vertebra was measured on the corpus calcareum long a straight line through the focus of each vertebra with SigmaScan Pro 5.0.0 Software (Systat Software, Palo Alto, CA, US). The size of the embryo’s centra and the birth band coincided furthermore, no pre-birth bands were observed. Additionally, a centrum of a 12.4 cm TL near-term embryo was polished and compared with a thin section of an adult. The birth band was defined as the angle change on the centrum side.
The sections were illuminated using reflected light on a dark background and submerged in a thin layer of water to improve the observation. Thin sections were observed under a stereo microscope (Olympus SZX9) and digitized using a video camera (Sony CCD-IRIS-RGB). Subsequently, sections were cleaned with scalpel and water and then dried at room temperature. Sagittal sections of 0.4 mm thick were made using double saws fitted with diamond-impregnated blades, ensuring that the focus of the centrum was included. Centra were fixed on wooden structures using a cyanoacrylate-based adhesive. However, none of the dyes tested presented an improvement in the clarity of growth bands thus, vertebrae were instead prepared as follows. Staining was performed at different times of exposure, from 1 min to saturation. Three cutting thicknesses (0.3, 0.4 and 0.5 mm) and two dyes, Alizarin Red S (0.01 g/250 mL water) and Bismarck Brown Y (0.01 g/250 mL alcohol 95%), were tested to enhance the visibility of the centra growth bands. A qualitative analysis to test the effectiveness of diverse treatments to enhance the visibility of growth bands was evaluated.
Cleaned vertebrae centra were dried at room temperature. Vertebrae were thawed, excess tissue manually removed and individual centra were separated using a scalpel. In Bahía de La Paz, an artisanal fishery on batoids captures around 14 species, among which N. In all these study cases, Narcine entemedor (Jordan and Starks, 1895) have been reported with low abundances nevertheless, Villavicencio-Garayzar and Márquez-Farías reported that they are commonly captured in artisanal fisheries of Mexico, especially during spring and summer. In Mexican elasmobranch fisheries, the main species of batoids captured are benthic, such as Pseudobatos productus, Zapteryx exasperate and Hypanus dipterurus, although some pelagic species such as Pteroplatytrygon violacea and Myliobatis californica have been found frequently in the catch. Many studies on the age and growth of elasmobranchs have been encouraged by the increasing exploitation of this group, which has been documented by numerous researchers, reporting the important effects of fishing mortality on batoid populations.
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