Number and biomass of fishes in the Nitra River (Slovakia) under anthropic influences
1997
Stranai, I. (Slovak Agricultural Univ., Nitra (Slovak Republic). Dept. of Poultry and Small Farm Animals)
At 26 localities of the Nitra river (Slovakia) fish were sampled to determine species composition, stocking amount and biomass density. 30 species of fish were found, a maximum of 9 species in the upper reaches of the river, 10 species in the middle section and 15 species in the lower stretches. Numerical and biomass densities were as follows: in a submontane creek (151-160 r.km) 5680 individuals and 330 kg per ha; in a submontane river (141-149 r.km) 3650 and 314 kg per ha; the river between 79-135.5 r.km is without fish, the sole individuals being recorded close to tributaries; within the middle parts of the river lies the best-stocked section (between 54-79 r.km) with a maximum of 13,900 individuals per ha and a biomass density of 720 kg per ha; the next 15 km of the water course (ranging from 33.5 to 54.5 r.km) is practically without fish; between 33.5-27.5 r.km the amount of fishes reached 3100 individuals with a biomass of 265 kg per ha; and finally the confluence up to 16 r.km accounted for a higher biomass density (715 kg per ha) owing to increased migration of fishes
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