MORTALITY, GROWTH AND DIET OF PERCH PERCA-FLUVIATILIS L IN THE CIKOLA BRANCH SYSTEM OF THE SZIGETKOZ AREA, RIVER DANUBE

Mortality growth and food composition were studied in perch of the Cikola branch system, River Danube, Hungary between 1988 and 1990. The instantaneous and annual mortaliy rates were high: Z = 1.448 and A = 0.765, in males respectively and the respective rates were Z = 0.759 and A = 0.532 in females. Back-calculated lengths from the radius of scale annuli revealed that growth of perch was wery slow, but the rate of growth in females was greater than males, the difference being significant (p = 0.01) for age groups greater-than-or-equal-to 4 +, when average length was 128 mm in males and 144 mm in females. The largest specimen was a 7 + female reached 223 mm. Stomach contents from 319 specimens contained mostly benthic organisms (Chironomidae and Trichoptera grubs, Malacostraca). Classification of the stomach contents revealed three main groups of characteristic food components: fish, chirononida, planktonic organisms. The high mortality and slow growth of perch were attributed to the high density of zooplanktivour cyprinids and perch themselves, and the shortage of refuge for older age groups during the low water levels.