cjs-200401-0007 ArticleInAPeriodical 2004 Czech Journal of Animal Science 49 1 43-50 NaminIJ SpurnýP. Fish community structure of the middle course of the Bečva River Fish communities of the Bečva River were studied in summer and autumn 2000 and 2001. Electric fishing gear (Honda EX 1000, DC 230 V, 0.75-0.9 kW) was used for sampling. Four sampling sites (Grymov 19.6 r. km, Rybáře 35.8 r. km, Hustopeče 50.7 and Choryně 54.7 r. km) were selected. Total of 23 fish species representing 5 families were determined. The family Cyprinidae with 15 species was dominant while Salmonidae, Balitoridae, Percidae and Gadidae were the other recorded families. Species diversity ranged from 9 at Hustopeče to 20 at Grymov localities. The lowest biomass and abundance were observed at Hustopeče locality (28.93 kg/ha and 336 fishes/ha) and the highest at Choryně locality (612.90 kg/ha and 7 367 fishes/ha). Barbus barbus, Chondrostoma nasus and Leuciscus cephalus contributed 87.73-97.55% and 60.5%-87% to total biomass and abundance in different samplings, respectively. The Chondrostoma nasus population was dominated by fish of total length over 300 mm. We believe that river fragmentation, trapping and blockade of fish are the main reasons for this irregular distribution. Index of diversity ranged from 0.811 to 2.05 and equitability index from 0.449 to 0.821. Physical and chemical parameters were also measured, pH value ranged from 7.8 to 9.8, DO (7.62-12.15 mg/l), conductivity (450-639 µS/cm), N-NH₄ (0.65-2.39 mg/l), P-PO₄ (0.12-0.68 mg/l)and alkalinity (2.55 to 3.40 mg/l).