–  Since the 1980s, the European eel Anguilla anguilla stock is in steep decline. Lipid reserves are essential to cover energetic requirements for silver eel migration and reproduction. Two large and independent data sets from Belgium and The Netherlands show an average one‐third decrease in fat contents of yellow eels over the past 15 years. Also Le Cren’s relative condition factor decreased. On the basis of the somatic energy reserves, reproductive potential of eels from various latitudes over Europe was estimated, assuming fat levels in yellow eel are indicative of those in silver eels. Only large individuals, females as well as males, with high lipid content seem to be able to contribute to the spawning stock. The decrease in fat content in yellow eels may be a key element in the stock decline and raises serious concerns about the chances of the stock to recover.

European eel (Anguilla anguilla (L.)) stocks are in decline in most of their geographical distribution and their status is considered below safe biological limits. Recently, there is an increasing awareness that spawner quality might be an essential element in the decline of the species since pollution by bioaccumulating chemical substances may have a large impact on the reproduction success of the eel. This review gives an overview of the literature on the effects of contaminants on the European eel and on the consequences on the biology and fitness of the eel in order to document the role of pollution in its decline. A variety of contaminants have been found to affect the eel. These contaminants may cause disturbance of the immune system, the reproduction system, the nervous system and the endocrine system and effects were reported on several levels of biological organization, from subcellular, organ, individual up to even population level. More extensive research is needed in order to evaluate how pollutants are detrimental to eel populations. Getting a comprehensive overview of the quality (including contamination levels, biomarker responses, lipid content and condition) of the silver eel population all over Europe seems to be an essential and urgent objective for the European eel management.

The existence of two morphotypes, broadheaded and narrowheaded, in European eels Anguilla anguilla is common knowledge among fishermen and eel biologists in Europe. To test whether European eels really are dimorphic in head shape, a total of 277 specimens from two locations in Belgium (Scheldt-Lippenbroek and Lake Weerde), in combination with a larger data set of 725 eels from river systems across Flanders (the northern part of Belgium) were examined. Our biometric data support the hypothesis that a head shape variation in 'Belgian' European eel is best described as having a bimodal distribution. Literature data suggest that this may be the result of phenotypic plasticity related to trophic segregation between morphs.

No abstract

No abstract