Relation entre la densite des microstries et le rayon de l'otolithe compatible avec le modele de von Bertanlanffy: application a Lutjanus sebae (Cuvier, 1828) aux Seychelles
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The age study of fishes using daily growth increments DGI observations is made from: 1- either the exhaustive determination of increments, 2- or the calculation of daily growth increments density for different otolith zones between the nucleus and the margin edge of otolith, the width of increments being presumed constant for each zone. To apply the first method, increments may be readable individually from the nucleus to the margin edge of otolith. This is a very time consuming operation. It can cause miscalculation of increments and errors of the age estimation. The second method, called "DGI density method" is based on the decrease of the increment width in relation to the slowing down of the growth phenomena. The more used approach according to this method consists in the search of a relationship between the DGI density and the otolith radius. The fish age for an otolith radius RT is obtained with the numerical integration of this relationship. At the moment, relationships that were proposed in the literature were algebraically inconsistant with fish growth according to the von Bertanlanffy's model. In this work, we propose an expression, algebraically consitant with the von Bertalanffy's model. Age determination and growth modelling using this method have been studied for Lutjanus sebae in Seychelles. Otolith data (radius, width of DGI zone, number of increments) have been collected with software for assisted acquisition of sclerochronological data developed on an image analysis station.