Ecological fish production in two small lowland rivers in Poland

Estimates were made of the ecological fish production in two small lowland rivers uninhabited by salmonids. Eight sites were examined in the Utrata River drainage basin, and five in the Zalewka Brook. Nets were placed at the upper and lower limits of each site and fish were captured using electrofishing apparatus; at the four sites estimates of fish density were verified by the use of rotenone. Twelfe fish species were found, the following being dominant: Three-spined Stickleback, Gasterosteus aculeatus L., Loach, Nemachilus barbatulus (L.), Gudgeon, Gobio gobio (L.). Ecological fish production ranged from 30.7 to 807.2 kg ha^-1 a^-1 (mean: 210.9 kg ha^-1 a^-1). Production was highest at the sites with the lowest number of species, the maximum value occurring in the headspring section with three species.