Juvenile paddlefish (age 0) used in these experiments, conducted in 1995 and 1996, were hatched from eggs collected from wild Missouri River adults (3♀ and 6♂ in 1995, 8♀ and 2♂ in 1996) and reared indoors at Gavins Point National Fish Hatchery, Yankton, South Dakota. For all experiments, ∼40–50 fish per tank were held in 1.8 m diameter circular tanks (stock tanks) containing 1320 l supplied with flow-through water. The water supply was a mixture of Lewis and Clark Reservoir water, passed through a drum filter and disinfected with ultra-violet irradiation, and well water. Specific conductivity of the water was 415 μS cm−1 and total hardness was 280 mg l−1 as CaCO3. Dissolved oxygen was consistently 9.5–10 mg l−1. Fish were left undisturbed and unfed for 24 h preceding each experiment