Existing data on Wałecki barbel are very scarce and need a complement to the quantitative description of its habitat conditions. This fish is a subspecies of the Pontic species B. cyclolepis Heckel which occurs in some coastal rivers of the Black Sea or, as evidenced by some results of studies on mitochondrial DNA, it is a hybrid originating from natural crossing between the common barbel Barbus barbus (L.) and spotted barbel B. carpathicus Kotlík, Tsigenopoulos, Ráb et Berrebi. Until now the Wałecki barbel was reported from 26 sites in the river basins of the Upper Vistula and the Dniester in SE Poland (49°09’–49°49’N, 21°28’–22°50’E, altitude 200–590 m). Seventeen of these sites were studied in autumn 2002 and summer 2003 to collect data on habitat parameters of stream channels. The main characteristics of their morphology (i.e. length, width, depth, and gradient) were calculated on the basis of a set of field measurements. Current velocity was measured using float method. The composition of bottom substratum was estimated using a simple scale based on Wentworth scale. Additionally, two biotic characters were included, i.e. the occurrence of macroscopic aquatic vegetation and the species composition of fish community. According to the obtained results the habitat conditions appropriate for Wałecki barbel may be defined as follows: 1) The stream should be medium-sized, at least 10-m or better 20-m wide. 2) The mean channel depth should exceed 20 cm, while the maximum depth should be greater than 50 cm. The channel morphology with the zone of medium depth (i.e. that extending over the half of bottom) in range between at least 15 and 40 cm seems to be favorable. 3) The mean stream velocity of 0.30 m s⁻¹ or more is desired. It seems that the zone of fast current (0.50– 1.00 m s⁻¹) sharing a considerable portion of the channel is an important habitat feature. 4) Most of the bottom area should be covered by mediumsized particles (2–200 mm) with the mode within range of fine pebbles (20–50 mm). 5) In general, the stream should be rather oligotrophic than eutrophic with poorly developed macroscopic algae and the absence of vascular plants, and with flow fluctuations periodically disturbing structure of bottom substratum. 6) The abundant occurrence of spotted barbel, especially within lower part of its distribution area and in the zone of its co-occurrence with common barbel may be regarded as a good indicator of the stream habitat appropriate for Wałecki barbel. 7) Other frequent and abundant species accompanying Wałecki barbel are minnow Phoxinus phoxinus (L.), stone loach Barbatula barbatula (L.), chub Leuciscus cephalus (L.) and schneider Alburnoides bipunctatus (Bloch).
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