1. Industrial Mathematics Institute, Johannes Kepler University of Linz, Altenbergerstr 69, 4040 Linz, Austria
2. Institute of Complex Systems, South Bohemian Research Center of Aquaculture and Biodiversity of Hydrocenoses, Faculty of Fisheries and Protection of Waters, University of South Bohemia-České Budějovice, Zámek 136, 373 33 Nové Hrady, Czech Republic