Swordfish, Xiphias gladius, is a billfish species subjected to intense exploitation in the Atlantic Ocean. Age determination and growth remain controversial notwithstanding their critical importance for fish stock assessment. Validation of aging procedures using hard parts has
not been accomplished. However, some questions are pending on the statistical protocols that have been used for that purpose. Statistically more robust protocols to test seasonal formation of marginal increments in anal fin spine segments are developed to show that a significant difference
in the growth of marginal increments exists during summer months relative to autumn and spring samples. A logarithmic formulation to back-calculate length at age generates more appropriate information on growth. Back-calculated lengths at age show that swordfish grow very rapidly during the
first year of life and then slow down considerably. Consequently, standard von Bertalanffy growth functions fitted to these data do not express growth correctly. A more flexible growth function improves the fit over the entire life span of the species.
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