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Group size influences light‐emitting diode light colour and substrate preference of David's Schizothoracin (Schizothorax davidi): Relevance for design of fish passage facilities

Fish passage structures have been constructed to facilitate fish movement past barriers, though the effectiveness of passage structures is highly variable. Designing fish passage structures that consider the behavioural preferences of fish under different environmental conditions (e.g., light colour, substrate type) has the potential to improve fish passage success. Similarly, whether a fish encounters a passage facility alone or in a group may influence fish behaviour. In this case, we assessed the preference of different group sizes (n = 1, 6 and 12, respectively) of David's Schizothoracin Schizothorax davidi under four different light‐emitting diode colours and eight different substrate types in the aquaria of the Houziyan Reproduction Station. We found that singletons preferred to visit the white light, cement and fine pebble, while the fish in groups preferred to visit the blue light, fine pebble and cobble. In addition, the total percentage of mobility frequency (18.3 ± 1.8%), movement velocity (20.4 ± 15.9 cm/s) and distance moved (15.8 ± 1.8 m) of singletons in blue light were much lower than that in the others. The movement velocity (3.3 ± 0.6 cm/s) of singletons on cobble was less, but the percentage of total mobility time (162.9 ± 16.0%) and distance moved (153.4 ± 19.6 m) on the cobble were much greater. Our research yielded novel insights for improving passage efficiency for this species. Findings from this study suggest there should be greater consideration of light colour and substrate type when designing fish passage facilities. Because fish almost always experience dynamic hydraulic conditions near and in fishways, additional research is needed to understand the generality of these findings in systems under lotic characteristics.