The effect of food-training on bigheaded carp challenging a multimodal deterrent

The geographic spread of invasive silver (Hypophthalmichthys molitrix) and bighead (H. nobilis) carp has prompted the development of several deterrents to limit upstream movement in river systems. One deterrent approach, combining CO₂ and broadband sound, has shown strong laboratory effectiveness in restricting upstream bigheaded carp movement through a model lock and dam. In the present study, the efficacy of the same deterrent was tested against bigheaded carp that were food-trained to transit upstream in the same laboratory environment. Schools of bigheaded carp (n = 10 fish per trial; 10–20 cm) were trained to swim through an open lock chamber to access food upstream. Following training, fish were simultaneously exposed to broadband sound and CO₂ in the lock chamber six times over two days to facilitate a conditioned stimulus. The effectiveness of broadband sound alone was then assessed for deterring food-driven bigheaded carp from transiting upstream during simulated boat passages. The deterrent remained highly effective, preventing 100% of food-driven bigheaded carp from transiting the lock to reach the upstream pool. These findings may provide insight for developing deterrent strategies and restricting fish under varying levels of motivational pressure from swimming upstream.