THE IMMIGRATION OF Anguilla anguilla (L.) GLASS EEL IN COASTAL WATERS: QUESTIONS ABOUT THE DETERMINISM OF THE OTOLITH STRUCTURES

Abstract

Glass eels were collected in estuarine and marine waters in the Bay of Biscay, in February and March 1992. Otoliths were examined with SEM for age and stages duration estimates. Major differences appear between successive samples of transparent glass eels (VB pigmentation stage): up to the „transition zone” the structures were similar, but the 1992 samples showed an additional marginal zone in most of the sagittae, even in transparent glass eels collected in deeper (40-60 m) offshore (60 km) waters. The ecological meaning of these final structures is complicated by: i) unknown determinism of the transition zone and ii) absence of a readable microstructure inside the marginal zone which excludes any back calculation.