Determination of resident brown trout Salmo trutta features by their habitat characteristics in streams of Serbia

Streams’ order, their width and depth, as well as the water temperature, conductivity, dissolved oxygen contents and pH reaction were recorded for 18 streams of the Danube River basin in Serbia that home brown trout Salmo trutta. For each of them, the number of fish species was recorded, and for brown trout in them the number of cohorts, age-structure, productivity (biomass, annual production and average weight) and growth (von Betalanffy’s growth parameters L∞, t0, K and ø’) were calculated. They were examined in relation to stream’s habitat features. Stepwise multiple regression revealed strong interdependence between habitat variables. Size, i.e., width and depth of streams increased and their oxygen content dropped with increase in their order and rise of the water temperature, and water conductivity was strongly interrelated with order and depth of streams. Increase in streams’ order and their water’s temperature were accompanied with the increase of species number in them, number of brown trout cohorts raised with the water conductivity and dropped with the increase of the alkaline pH value of streams, whereas growth of brown trout was determined by width of streams and their water’s conductivity. However, when analyzed one at a time, very few of habitat and population traits, e.g., stream depth and L∞, varied clearly in streams of either various orders, or conductivity classes, respectively. The notable, but not yet significant variability of almost all other characters implicates their strong and complex acting in concert to determining number of fish species in syntopy, brown trout population, productivity and growth features