Environmental correlates of fish distribution
Temperature (whole CCA test: 4.4 % of explained variability, pseudo-F = 7.0, p < 0.001), normalized water age (whole CCA test: 3.7 % of explained variability, pseudo-F = 6.0, p < 0.001) and ChlA (whole CCA test: 1.2 % of explained variability, pseudo-F = 1.9, p < 0.001) were significant environmental variables selected by Interactive Forward Selection procedure (Figure 6a, b). The first axis explained 7.07% of the variation, whereas the second and third axes explained 1.53% and 0.65% of the variation, respectively. Based on the ordination score, the first axis is mostly correlated with temperature, where some taxa prefer high temperature (e.g. pumpkinseed [Lepomis gibbosus ], wels catfish), some taxa are flexible (e.g. bleak, freshwater bream, white bream [Blicca bjoerkna ], roach, ruffe [Gymnocephalus cernua ]), and other taxa prefer cold water (e.g. all salmonids, bullhead [Cottus gobio ],Coregonus spp., Lampetra spp., stone loach [Barbatula barbatula ], topmouth gudgeon [Pseudorasbora parva ]). The second axis was predominantly correlated with normalized water age, separating taxa detected in the deep lacustrine part with longer retention time (e.g. prussian carp [Carassius auratus gibelio ]) from those detected near the river inflows (e.g. bullhead, Coregonus spp., grayling [Thymallus thymallus ], gudgeon [Gobio gobio ],Lampetra spp., stone loach). Finally, the third axis correlated with the proxy of the trophic gradient, with European eel (Anguilla anguilla ), pumpkinseed and wels catfish detection in more trophic habitats, and prussian carp and Coregonus spp. detected in nutrient-low environments.