Swimming performance and behaviour of bighead carp (Hypophthalmichthys nobilis): Application to fish passage and exclusion criteria

The bighead carp (Hypophthalmichthys nobilis) is one of the most commercially important freshwater fish species in China, but their abundance has declined considerably in recent decades, partly due to river regulation. In other countries it is invasive, posing an ecological and economic threat. To improve fish pass effectiveness at impediments to migration in its native range, and create velocity barriers to reduce range expansion where it is invasive, an improved understanding of swimming ability and behaviour is needed. The burst, prolonged, and sustained swimming performance of juvenile bighead carp were quantified experimentally through constant acceleration trials (Umax), fixed velocity tests, and volitional passage efficiency trials through three consecutive constrictions. The effects of fork length (FL), temperature, swimming speed and method (swim chamber/open channel flume section) on endurance in fixed velocity trials were evaluated. The utilisation of low velocity areas close to the flume edge and floor at different mid-channel velocities was also explored. The mean sustained swimming speed in endurance tests was 3.84 FL s−1 (range equivalent to 0.37–0.78 m s−1), and burst speeds reached 12.78 FL s−1 (up to 1.22 m s−1 for larger fish). The meanUmax was 6.81 FL s −1 (0.51 m s−1). In fixed velocity trials, method did not influence endurance and fish rarely utilised low velocity areas in the corners of the flume when water velocity exceeded sustained swimming ability. Passage efficiency decreased at successive flume constrictions, possibly indicating a poor repeat burst swimming performance. Field validation is required to verify wild bighead carp behaviour and passage in the hydraulic conditions created by fish passes.