Abstract: Culverts are important in maintaining surface water flow and guaranteeing the integrity of the local water habitat, and thus providing gene exchange channel for the majority of migratory fish. As an important factor affecting the efficacy of culvert fishways, the darkened environment in the culvert barrel partly delays the ascending migrants, impairing the passage performance for target fish. We set up typical light conditions in a physical culvert model and conducted an experiment with Schizothorax prenanti, a coldwater species with economic significance in China. We examined the behavioral strategies and upstream swimming of S. prenanti in the culvert passage under different light treatments, including two colors (white light and green light), three illuminance levels (10-100 lx, 100-1000 lx, and above 1000 lx), and the control group of total darkness, by measuring the attempts, attempt success rate, and the distribution within and outside the culvert. The attempts of fish in the green light treatment of 100-1000 lx were significantly higher than that in the green light of 10-100 lx (P=0.009) and white light of the same illuminance (P=0.044). The change of illuminance and color settings did not affect attempt success rate of S. prenanti (P=0.819). The white light motivated the attempts of test individuals into the culvert at the illuminance range of 0-1000 lx, contributing to the successful pass with a certain probability, while it sparked the escapes at above 1000 lx. The green light of 100-1000 lx substantially increased the proportion of S. prenanti reaching the upstream of the culvert (22.50±8.74)% while trapped the fish in the barrel at above 1000 lx, reduced the ratio to (16.44±4.01)%. Our study provided an optimizing strategy for culvert fishway, i.e. alluring the target fish into the entrance with the green light of 100-1000 lx and then accelerating the passage using white light of 1000 lx.

Key words: light environment, culvert fishway, phototaxis, upstream migration.