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The butterfly ray, Gymnura marmorata (Cooper, 1864), is a demersal species caught by artisanal gillnets fishery. However no information exist regarding the estimation of the growth parameters for this species in the western coast of B.C.S. The age determination and description of the growth of marine organisms provide valuable information for demographic parameters, which are used for management of marine resources. The samples were obtained from artisanal fishing. The organisms were measured (disk width) and sexed. A section of vertebrae of the thoracic region was removed. Longitudinal cuts of 0.4mm in vertebra were performed to show the pattern of bands. The growth bands were read, and formation time of the growth marks was estimated, using the edge type analysis and the marginal increase analysis (MIA). Growth curves were made for G. marmorata by sex and the growth model was selected based on the Akaike decision criteria. 167 vertebrae of G. marmorata (with a sex ratio of 2: 1 female-male) were analyzed, with a size structure from 340 to 1330 mm disk width (DW), covering almost the entire length interval reported for this species. Three independent counts were made by two readers; the accuracy and bias tests were consistent with those mentioned in the literature (APE = 3.22%, CV = 4.64%). Based on MIA test results the periodicity formation of the growth marks was assumed in approximately 12 months. The maximum ages observed were 5 and 13 years for males (780 mm DW) and females (1330 mm DW) respectively. According to the comparison of the values of the Akaike information criterion (AIC), it was determined for males using the von Bertalanffy growth model (3 parameters), as the best fit with respect to the data (DW8 = 758 mm, k = 0.54 year-1, t0 = -1.55 year) and the Gompertz growth model (3 parameters) for females (DW8 = 1269 mm, k = 0.25 year -1, t0 = -0.19 year).

Palabras clave: Gymnura marmorata; vertebrae; marginal increase analysis; age determination; growth description; growth models; Akaike information criteria

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