To maintain a constant position against the rotational current, the fish were forced to swim no faster than the mean rotational velocity of the culture water, which was 18.4 ± 0.2 and 18.3 ± 0.3 cm/s for the high and low NO3-N treatments, respectively; but average swimming speeds for both treatments exceeded 36 cm/s (approximately two times faster than the water rotational velocity).