This thesis describes the food, foraging and growth of the eel (Anguilla anguilla). Attention is paid to the abundance and distribution of the food organisms and the feeding and growth of other fish species. The investigations were carried out in the Tjeukemeer (21 km2) in the northern part of the Netherlands. This lake is the main object of study of the Tjeukemeer laboratory, part of the Limnological Institute of the Royal Netherlands Academy of Arts and Sciences. The Royal Academy funded the research on eel, the Ministry of Health and the Environment funded the zooplankton research.The Tjeukemeer is a shallow (1-2 m) , turbid (Secchi-disc 0.30 - 0.40 m), hypertrophic lake. It is part of a system of canals and reservoirs (lakes) receiving surplus water in late autumn, winter and early spring from a watershed covering 3060 km 2. Via this system the water is drained into the Waddensea or pumped into the IJsselmeer. When during spring and summer the evaporation exceeds precipitation, the whole system is drained with water from the IJsselmeer. These inputs have great impact on the physico-chemical conditions, but also on the fish fauna of the lakes. The smelt (Osmerus eperlanus) immigrates passively from the IJsselmeer as a massive flow of larvae. This immigration is dependent on weather conditions, therefore the abundance of the smelt is highly variable.The shoreline of the Tjeukemeer is poorly developed, the emergent vegetation covers 0.5% of the surface; since the early 1970s the submerged aquatic vegetation is greatly reduced and now virtually absent.The eel population in the Tjeukemeer, like in other large Dutch lakes, is heavily exploited. The population is dominated by small eels between 200 and 300 mm. Eels smaller than 120 mm are scarce. The proportion of eels larger than 300 mm ranges between 7 and 30% of the catch.Irrespectively their body length, the eels prefer as food invertebrates, at least 7 mm large, living on the water bottom surface. In the Tjeukemeer the larvae (later instars) and pupae of the ...