Positive phototaxis in larval bonytail

Abstract

We conducted an experiment to determine phototaxis in bonytail Gila elegans, a Colorado River basin endemic fish. We tested groups of 50 protolarvae (6.1-8.9 mm total length) in darkness for 2 h or 4 h with illuminated (lighted) and nonilluminated (unlighted) traps suspended in aquaria in pairs (one lighted and one unlighted, two lighted, or two unlighted); we repeated each trial three times. Among all trials, lighted traps captured 60% (359 of 600) of available larvae, which was significantly more than the 0% (1 of 600) from unlighted traps. Results demonstrate positive phototaxis and suggest larval light-trapping could be used to detect the presence of larval bonytail or to monitor or collect individuals for management of this critically imperiled species.