A comparison of growth rates of rainbow trout in culture tanks with different hydraulic characteristics

The differential performance of rainbow trout (Salmo gairdneri) in small scale models of circular cross-section raceways, circular tanks, and vertical tanks were documented. The experimental tanks had a water volume of 47 liters each. A constant head reservoir supplied water to the culture tanks equally at a flow rate of 5 l/min. The fish with initial weight of 9.08 g (9.11 cm) were reared through 4 periods of 42 days each (August 14, 1981 January 31, 1982). For every period, the tanks were stocked with the same number of fish. All fish lots were fed equal daily ration at the same feeding frequency. The feed ration ranged from 3.0% to 0.8% body weight per day. The water temperature fluctuated from 17°C to 4°C. Water pH was consistently on the acid side with a low level of 5.1. Total ammonia levels were negligible with a high of 0.73 mg/l. The heaviest stocking density attained was 171.68 kg/m3. The calculated pond loading indices, Wi, ranged from 0.63 to 1.45 kg/l-cm while the carrying capacities ranged from 0.35 to 1.61 kg/l/min. The average weight of the heaviest fish lot at the end of the study was 101.80 g (19.94 cm). The tanks and growing periods were compared on the basis of percent weight gain, length gain, condition factor, and feed conversion ratio. The two-way analysis of variance showed significant variation from tank to tank and from growing period to growing period in everyone of these growth parameters. For all 4 periods, the percent weight gains and length gains in the vertical tanks were consistently the highest. The raceways gave the least gains. Feed conversion efficiencies were highest in the vertical tanks and least in the raceways. Feed conversion ratios varied from 1.23 to 2.93 kg of feeds/kg of fish. For a given length, the fish in the vertical and circular tanks were heavier than those in the raceways. The observed condition factors ranged from 0.0123 to 0.0133 g/cm³. The results of tracer experimentation confirmed that the circular tanks approximated an ideal mixed flow and that the raceways approximated an ideal plug flow. The vertical tanks exhibited hydraulic properties similar to those of the circular tanks indicating mixed flow conditions in the tanks. Correlation between growth rates and hydraulic characteristics indicated that growth rates are higher in mixed flow tanks than in plug flow tanks. The hydraulic studies also showed that fish biomass and activity significantly affected the hydraulic characteristics of the culture tanks.Applied Science, Faculty ofGraduat