Swimming performance of adult bighead carp Hypophthalmichthys nobilis (Richardson, 1845) and silver carp H. molitrix (Valenciennes, 1844)

Summary Although the movement of invasive bighead carp (Hypophthalmichthys nobilis) and silver carp (H. molitrix) in the Upper Mississippi River system is dependent on their ability to swim through its numerous lock-and-dams, the swimming performance of adults of these species is at present unknown. Using a large (2,935-L) mobile swim tunnel, the swimming performance of adult bighead and adult silver carp was quantified at water velocities that challenged them to exhibit either prolonged and/or burst swimming (76–244 cm/s) with fatigue times of less than 10 min. Simple log-linear models best described the relative swim speed to fatigue relationships for both species. Under these conditions, the swimming performances of adult bighead and silver carp were similar to several species of adult fishes native to the Mississippi River system, but relatively low (<3 total body lengths per second, TL/s) compared to previously studied juveniles and sub-adult bigheaded carps (3–15 TL/s). The decline in endurance with water velocity was three times greater in bighead carp (slope = −2.98) than in silver carp (slope = −1.01) and the predictive ability of the bighead model was appreciably better than the silver carp model. The differences in adult swimming performance between the two species were coincident with behavioral differences (e.g. breaching in silver carp but not in bighead carp). The swimming performance data of adult bighead and silver carp can now be used to evaluate whether their passage through manmade river structures including the gates of lock-and-dams in the Upper Mississippi River might be reduced.