The evaluation of hydraulic characteristics of some fish culture tanks.

In search for the most efficient type of tank for the culture of rainbow trout, the hydraulic characteristics of small-scale cross-section raceway, circular and vertical tanks were evaluated using the pulse-response method of tracer examination. The results indicated that the raceway was significantly different from the circular and vertical tanks in terms of mean residence time, dead volume, and variance of the exit age distribution curve. The mean residence time in the raceway was significantly longer than those in the other two tanks. For all the three types, it takes more than twice the theoretical mean residence time to completely change the water. The dead volume observed in the tanks had the following ranges: raceway — 1 to 11 percent; circular tank — 11 to 31 percent: vertical tank — 15 to 34 percent. The dead volume in the raceway was significantly smaller. The variance data together with the exit age distribution curves show that the raceway approximates the ideal plug flow type of tank — while the circular and vertical tanks both approximate the ideal mixed flow type of tank. On the premise that either one of the two ideal types of tank would prove most efficient for the culture of any given aquatic species, engineering efforts should be directed towards improvements in tank design that enhances the similarity of existing culture tanks to the ideal types