Comparison of raceways of circular and rectangular cross-section for the culture of rainbow trout (salmo gairdneri)

Fish raceways of different cross-sectional shapes were compared in biological and hydraulic tests. Raceways of rectangular and circular cross-section were used. Two types of circular raceways were studied, one with a smooth wall, made of PVC, and one with a corrugated wall, made of galvanized steel that had been painted. The biological tests consisted of comparing the weight gain of rainbow trout (Salmo gairdneri) fingerlings (initial weight 6.0 g) held in the different raceways for 69 days. The fish in the painted corrugated steel raceway (final weight 25.6 g) grew more than those in the rectangular (final weight 22.9 g) and PVC (final weight 20.2 g) raceways (significant at α = 0.05). Very high stocking densities (130-139 kg/m³) achieved at the end of the experiment. Critical concentrations of dissolved oxygen or ammonia had not been reached at this point. Two types of hydraulic tests were done. One consisted of flow visualization studies in which a dye, malachite green, was introduced into the raceway and its movement observed and recorded photographically. In the second hydraulic test, the concentration of malachite green in the effluent was measured at various times after the introduction of the dye. These data were then used to obtain residence time distributions for the various raceways. No major differences were found between the hydraulic characteristics of the raceways tested. A biological test using unpainted galvanized corrugated steel raceways was also carried out. Rainbow trout fingerlings (3.6 g) were placed in galvanized raceways that had been flushed for 64 days. The fish were left in the raceways for 29 hours. During this time, 48% of the fish died. The survivors were transferred to fiberglass tanks where an additional 27% of the fish died over the next 50 hours (2 days).Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat