here are two citations that include information on microhabitat selection
in Barbus graellsi and Barbus haasi in Spain,  Grossman & deSostoa 1994
Ecology of Freshwater Fish 3:123-136, and 3:141-152.  There isn't much
info on habitat selection for european barbus, but there are some papers
listed in the literature cited section of those papers.  In addition, I
think that Gordon Copp has done some studies in france and perhaps fritz
Schiemer and Irene Zweimuller in Vienna.  Also Henri Persat or someone
else in that big stream group at Univ. of Lyon (e.g. Yves Souchon, or B.
Hugueny, or J. Baglianiere) might have information on habitat selection
in european barbus.  You probably also know Javier Lobon-Cervia and
Pedro Rincon at the Museo Nacional des Ciencias Naturales in Madrid,
they also do quite a bit of microhabitat work on spanish fishes
(along with Adolfo de Sostoa at the University of Barcelona), so if you
don't, they also would be worth contacting. sincerely, gary grossman