Age, growth, and condition of European eel (Anguilla anguilla) from six lakes in the River Havel system (Germany)

A total of 199 female yellow European eels (Anguilla anguilla), 21.6-66.2 cm long and 3-14 years old, was collected by electro-fishing from six lakes in the River Havel system (Germany) in spring 2001. The condition and the growth rate, estimated by otolith increments, varied between eels within single lakes and between lakes. Fulton's condition factor ranged from 0.10 to 0.24 and the gross energy content varied between 4.3 and 15.3 MJ kg(-1). There were no significant differences in mean condition factor (0.16-0.18) or gross energy content (6.5-9.3 MJ kg(-1)) between lakes. Fastest growth was in Lake Blankensee (mean 5.3 cm year(-1)), and the slowest in Lake Sacrow (mean 4.0 cm year(-1)). For all lakes combined, the overall mean annual increment was estimated to be 4.5 cm year(-1). The biggest annual increment on the otoliths was generally laid down during the first and second years in fresh water, when the growth rate was 6.1-8.5 cm year(-1). Then, in the subsequent 12 years, the annual increment remained almost constant or decreased slightly (with lake-dependent values of between 1.6 and 6.8 cm year(-1)). In the River Havel system, the time between stocking of the lakes with glass eels and the recapture of eels at 45 cm body length was 7-10 years. The physiologically possible maximum length (L infinity values) of eels lay in the range 50-130 cm. In comparison with previous investigations (between the 1950s and the 1970s), the only difference observed was a trend towards slower growth.