AGE-DETERMINATION OF EELS IN THE FRENCH MEDITERRANEAN LAGOONS USING CLASSICAL METHODS AND AN IMAGE-ANALYSIS SYSTEM

Several methods are used for age determination of eels in the French mediterranean lagoons (observation of the whole otolith after clearing, grinding and polishing, dyeing, SEM and image analysis). Two types of otoliths are observed depending on the width of the growth rings which is probably related to the environmental conditions. Furthermore, the growth checks are located nearby or inside the opaque rings. A computer assisted method is developed, with reference to the other methods, with the aim of improving the efficiency of collecting and processing age and growth data. With further developments and increasing knowledge of the life-history of elvers and juvenile eels, it seems possible to use an image analysis system for ageing eels in lagoons. Nevertheless, the most important point is to validate the results before using them for growth populations studies.