Troubled by the humics — effects of water colour and interspecific competition on the feeding efficiency of planktivorous perch

In humic lakes in addition to various density-dependent interactions, dark water may be partly causing a bottleneck in perch (Perca fluviatilis) growth. This study focuses on clarifying the role of water colour and increasing fish density on the plankton feeding efficiency of perch. Both aquarium experiments and field data were used in this study. In the experiments, perch fed clearly less in highly humic water than in clear water, but the presence of roach had no significant effect on the feeding efficiency of perch. According to the field data, water colour had a significant effect on the length at which perch shifted from feeding primary on plankton to other food sources.