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The aim of this study was to assess the suitability of different vertebrae staining techniques for the visualization and counting of growth bands in tropical species of batoids (Narcine leoparda, Urotrygon aspidura, Hypanus longus, Potamotrygon magdalenae) and sharks (Alopias pelagicus, Carcharhinus falciformis, Sphyrna lewini, Sphyrna corona and Mustelus lunulatus). Different cutting thicknesses and staining protocols were tested, analysing the precision and bias of each combination to identify the most accurate technique for estimating age. Vertebral sections of 0.4 mm were more suitable for batoids, except for Narcine leoparda; for this species and for all the shark species assessed, sections of 0.5 mm are recommended. Different combinations of stain and exposure time were required to achieve the best visualizations of vertebral growth band pair for the shark and ray species. Intraspecific variation occurred among vertebrae size of batoids. Our results confirm the importance of defining a suitable species-specific protocol for sectioning and staining hard structures before carrying out an age and growth study to improve the reliability of the age estimates.

Mathematical formulas and abbreviations of the individual growth models adjusted to the estimated age data for Panamic stingrays (Urotrygon aspidura). The parameter DW ∞ is the theoretical asymptotic size, representing the average disc width at age that individuals in a stock would attain if they grew indefinitely. The parameter k 1 is the relative annual growth rate, which is a curvature parameter determining the rate at which a stingray reaches the asymptotic size at age and which decreases linearly with DW, and t 1 is the theoretical age at zero, which defines the initial condition on the time axis when mean DW at age is zero. The parameter k 2 is the annual rate of exponential decrease of the relative growth rate (λ) with age, and t 2 is a parameter corresponding to (lnλ−lnk 2 )/k 2 . The parameter k 3 is the relative annual growth rate, and t 3 is the inflection point of the sigmoidal curve. The parameter t h is the age at which the transition between the 2 phases occurs (inflection point), and h is the maximum difference in size at age between the von Bertalanffy and two-phase growth models at the t h . The parameter DW o is the mean DW at birth (fixed at 7.5 cm for models with 2 and 4 parameters).

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