FOOD BIOLOGY OF THE FISHES IN THE DYJE RI VER UNDER WATERWORKS AT NOVE-MLYNY

The Dyje river was known by its fish richness in the past. Carp, pike and some other fishes breeded at spring floods. The quality of water d ecreased owing to pollution and quantum of fishes declined to 10% orig inal quantity after the year 1960. After construction of the waterwork s the quality of water was improved and quantity of natural food incre ased in the lower part of the river. Improvement of the environmental conditions of the fishes led to an increasing individual weight of fis hes (see Tab. III). The food biology of some fish species (white bream , roach, rudd, ide) was studied in the lower part of the Dyje river. T he material investigated was obtained by angling. The food analysis sh owed these results. The most significant food component of white bream were Cladocera, followed by detritus and filamentous algae. A large p roportion in the gut content of roach was composed of filamentous alga e and detritus followed by Cladocera and larvae of chironomids. The fo od spectrum of roach was similar to that of rudd arid ide. Food compos ition of caught fishes is given in Tab. I. Food competition expressed as percentage of food similarity in the studied fishes is given in Tab . II.