ABSTRACT
Flowing water fish culture is conducted in one of two general types of rearing units that differ in their hydraulic characteristics. Linear units, usually called raceways, exhibit a hydraulic pattern that approximates plug flow in which all elements of the water move with the same horizontal velocity. Circulating units, such as round tanks, have non-uniform velocities and new water is added to a mass of circulating, used water. Thus, linear units containing fish exhibit a water quality gradient from the inlet to the outlet, while circulating units have relatively uniform water quality at all positions. Linear units have uniform water velocity, while circulating units exhibit a velocity gradient as water velocities are highest at the outer rim and decrease toward the center drain.
