LOW-FAT CONTENTS IN FEMALE SILVER EELS - INDICATIONS OF INSUFFICIENT ENERGETIC STORES FOR MIGRATION AND GONADAL DEVELOPMENT

The main energetic stores at the silver eel stage were studied by anal ysing muscle fat concentrations and hepatosomatic indices in female si lver eels from various habitats in Sweden. Muscle fat concentrations v aried both within and between localities and lean eels with muscle fat concentrations <20% occurred at all study sites. Furthermore, no corr elation could be found between muscle fat content and internal or exte rnal maturation indices, neither was the relative liver size related t o the maturation process, as the correlation between the hepatosomatic and gonadosomatic indices was very weak. Consequently, it was conclud ed that silvering and the spawning migration may begin also at low mus cle fat concentrations. However, most of the energy reserve is stored as muscle fat in eel, and it is highly unlikely that female silver eel s with such low fat contents, as were observed occasionally in this st udy, will ever recruit to the next generation. Therefore, it is sugges ted that the maturation process in eel is more flexible than previousl y recognized, and that this process might be temporarily arrested and feeding resumed during the first part of the migratory phase. (C) 1997 The Fisheries Society of the British Isles.