Relation entre la densité des microstries et le rayon de l'otolithe compatible avec le modèle de von Bertanlanffy: application à Lutjanus sebae (Cuvier, 1828) aux Seychelles

Daily growth increments (DGI) density - otolith radius relationship according to the von Bertanlanffy's growth model: application to Lutjanus sebae (Cuvier, 1828) in Seychelles. Often, age determination of fishes is conducted from several parts (scales and otoliths for teleost fishes, vertebrae, spine, opercular bones, ...) displaying seasonal marks (annuli) associated with growth checks, which can be used for the estimation of individual age. Since Panella's (1971, 1974) discovery of the daily growth increments (DGI) in the teleost otoliths, age determination with DGI method has been used more and more on larval stages of both temperate and tropical species and juvenile and adult individuals of, principally, snapper and grouper species. The age study of fishes using 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 Bertalanffy's model. In this work, we propose an expression, algebraically consistant with the von Bertalanffy's model.

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