Further faunistic and ecological investigation of the lamprey and fish fauna of the Mlava River upper course

Abstract

The 1996 summer season, an investigation of the Mlava River upper course was performed using the same methodoloty as in the previous investigation (late autumn season of 1995), in order to supplement the data on the brown trout distribution. Correspondence analysis was done in order to make an objective characterization of upper course fish cenoses. In relation to previous investigation, two new cobitid species were found, e. g. the stone loach Barbatula barbatula (Linnaeus, 1758) and the Balkan loach Cobitis elongata Heckel & Kner, 1858. Apart from certain movements of particular fish species between sampling profiles, their distribution mostly confirmed previous expectations. Thus, the two upper profiles (i.e. upper and middle ones) could be denoted as salmonid region, whereas the lowest profile is transitional, i.e. the barbel region. The effect of salmonid fish-farm at the spring of the Mlava River to the brown trout seems negligible, in spite of the evident deterioration of water quality according to chemical and microbiological parameters. It seems that main reason for the limited distribution of brown trout is gradual increasing of the water temperature. It is to be considered that this brown trout population is separated from others, from the distant downstream tributaries of the Mlava River middle course, but the confirmation of that premise needs further investigations.