Growth-in-Length of Eurasian Perch (Perca fluviatilis L.) in Gružansko reservoir before and after its formation

Abstract

Growth-in-length of the Eurasian perch (Perca fluviatilis L.) from the Gružansko Reservoir was investigated in 1991, on the sample of 152 fishes, by methods of Monastirsky, von Bertalanffy and Walford. The presence of particular age classes in the sample reflects the very diversified sample structure. Both observed, and calculated growth-in-length revealed that perch from this locality did not grow typically for the lake habitat, in comparison to the other reports from similar habitats, and regarding the geographical latitude of this reservoir. Therefore, the model of investigation was updated by taking into consideration the time of reservoir formation, i.e. some 16 years before the date of sampling. That clarified previous results, and revealed the presence of mixed stock of the older, initially more slowly growing fish, coming from the riverine habitat, and of the younger, fastly growing ones, hatched in the reservoir's lacustrine environment. Thus, the perch from the former River Gruža grew fastly, in comparison to data from similar rivers. However, perch from the reservoir grew slowly in comparison to available data for similar habitats.