1. Faculty of Economics and Management, University of Szczecin, 71-101 Szczecin, Adama Mickiewicza st. 64, Poland; and
2. Department of Hydrobiology, Ichthyology and Biotechnology of Breeding, West Pomeranian University of Technology, 71-550 Szczecin, Kazimierza Królewicza st. 4, Poland (ORCID: http://orcid.org/0000-0002-0899-720X [E.S.])