DRIFT OF LARVAL AND JUVENILE FISHES, ESPECIALLY RHODEUS-SERICEUS AND RUTILUS-RUTILUS, IN THE RIVER MORAVA (DANUBE BASIN)

Drift of larval and juvenile fishes in the lower stretch of the River Morava, a tributary of the River Danube, was monitored bi-weekly from late May until early August 1992. Six species of early stages of fish were recorded with bitterling Rhodeus sericeus (PALLAS) and roach Ruti lus rutilus (L.) being the most abundant (88.9 and 9.1%, respectively) . The abundance of drifting fishes peaked during the second half of Ju ne (843/100 m(3)) and markedly decreased in early August (8/100 m(3)). Roach larvae drifted earlier, with a maximum in late May, followed by bitterling, which peaked in late June. Larvae almost always migrated at night (day-twilight-night ratio was 1.0:0.5:110.3), in spite of low water transparency in the river. Drift was more abundant near the sur face (maximum intensity was at 23:00-3:00 hrs), than in bottom samples . Drifting roach larvae were significantly larger in early June than i n late May. Bitterling larvae drifting in June tended to be larger tha n those drifting later. Size distribution of fish with depth showed no regular pattern.