Dams and weirs fragment freshwater ecosystems, obstructing fish migration and threatening biodiversity in rivers globally. Modular pipe fishways offer a scalable, cost-effective ecological solution, however, fish attraction and passage into pipe fishways remains a critical challenge. Here, we investigated how pipe illumination can influence fish attraction and passage by combining controlled laboratory experiments and field trials.
An experimental laboratory study was conducted that tested the phototactic responses of three Australian freshwater species: Golden perch (Macquaria ambigua), Spangled perch (Leiopotherapon unicolor), and Olive perchlet (Ambassis agassizii). Fish were introduced into a hexagonal arena with six pipes illuminated by distinct coloured LEDs (red, yellow, green, blue, violet) or unlit (control). Preference to artificial coloured light (wavelength) was determined by the fish’s cumulative dwell time in each colour.
Complementary field trials evaluated passage preferences of wild fish in a freshwater creek in Sydney under ambient and partial daylight, and artificial full-spectrum daylight LED. Wild fish were guided into a pool where upstream migratory behaviour, driven by rheotaxis (orientation into flow), required passage through either the illuminated pipe or its paired dark (control) pipe. Over 3,500 fish, from 8 different taxa, ranging from 15 to 100 mm in total length were recorded.
The illumination treatments that observed the highest preference could be utilised in the entrance designs of pipe fishway to enhance attraction and passage. Outcomes assist in informing scalable solutions for restoring connectivity in fragmented rivers, supporting global freshwater conservation efforts.