I have to say that in principle I am against the stocking of barbel in still waters. However, when you look at the barbel species worldwide they can thrive in lakes that once were part of a flowing river before damming. I fish a 5 km length of the Vienne between two hydro dams and the barbel do very nicely. Same in Spain and the Middle East. Also, rainbow trout are basically land locked steelhead migratory trout and they thrive in some still waters so it isn't that cut and dried.