THE IMPACT OF PONDS AND HATCHERIES ON THE ICHTHYOFAUNA OF THE DOBRA RIVER (CENTRAL ODER RIVER TRIBUTARY)
Andrzej Witkowski, Paweł Paszkowski
University of Wrocław, Poland
ABSTRACT. Many fish species migrate through the supply streams of fish cultivation facilities (ponds, farms and hatcheries). These streams are the sources of so-called exotic species which are undesirable in open waters. They appear in the Dobra River when ponds are drained and during other hatchery works conducted in spring (April-May) and autumn (October-November). As a result, the number of species varies seasonally from six to 15. The ichthyofauna density increases from 1.70 to 124.94 specimens 100 m-2, while the biomass grows from 27.86 to 962.95 g 100 m-2. The majority of escapee fish belong to limno- and stagnophilous species. Most of these fish remain in this foreign environment only for a short time of 2 to 4 months.
Key words: LOWLAND RIVER, ICHTHYOFAUNA - SPECIES COMPOSITION, DENSITY, BIOMASS, IMMIGRATION FROM CULTIVATION FACILITIES
Andrzej Witkowski, Muzeum Przyrodnicze, Uniwersytet Wrocławski, ul. Sienkiewicza 21, 50-335 Wrocław;