Fish Production in Warmwater Streams in Poland and Ontario

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Abstract
Density (numbers per hectare), biomass (kilograms per hectare), and annual production (kilograms per hectare per year) of entire stream fish taxocenes were significantly higher at localities in Ontario (n = 11) than in Poland (n = 14). The production/biomass ratio and the mean size of individuals did not differ significantly between the two sets of localities. The average stream size at the localities studied in Poland was significantly smaller than in Ontario. Production and biomass in Poland showed a significant negative association with stream size, whereas in Ontario these relationships were not significant; therefore, the differences in these variables between Poland and Ontario may even be underestimated. Differences in fluvial fish taxocene richness might explain the observed differences in production if the streams in Poland are less saturated than those in Ontario. However, the possibility of more basic differences in productivity at lower trophic levels cannot be ruled out.