POPULATION-STRUCTURE AND REPRODUCTIVE STRATEGY OF THE WHITEFISH COREGONUS-LAVARETUS (L) IN 2 GREEK LAKES

The biology of C. lavaretus, an introduced fish species, was investiga ted in two contrasting environments, the oligotrophic manmade Lake Tav ropos and the mesotrophic to eutrophic Lake Vegoritis. Ageing of fishe s through the length-at-capture data and the length frequency distribu tion revealed three age classes in Lake Tavropos and four in Lake Vego ritis. Age III+ fishes dominated in the catches while age I+ and II+ c ontributed the least to the age composition, indicating a poor recruit ment and a not successful reproduction. The growth of fishes derived f rom the body-scale relation was similar but females from Lake Tavropos had lower condition b (derived from the weight-length relationship) a nd also were hypometric (less than 3). In contrast, ovary weight per l ength cubed was higher, with fewer but larger eggs being produced. Thi s reproductive strategy was connected with the oligotrophic status of the lake, in which the planktonic food for the larvae was low and is n eeded a larger size to cope with long periods of starvation, or even t o match the size of the preferred but scarce copepodites and nauplii. After twenty years of the species introduction and despite regular res tocking, the fish show poor fitness in the new environments. Stock ove rexploitation, lack of fishing policy and inattentive handling during the restockings, can partly explain why the species does not thrive.