Michigan Department Of Conservation
Institute For Fisheries Research Report No.1749, 1968
Growth Rates of Coho Salmon and Steelhead Trout with a Limited Food Supply
Percy W. Laarman
Abstract.-Competition between coho salmon and steelhead trout was studied by comparing specific growth rates of the two species in a laboratory raceway. The raceway was partitioned into six test compartments, each 5 feet long by 14 inches wide; each compartment had flowing water of about 45 gallons per minute with temperature averaging 57 F and dissolved oxygen 6.5 ppm. Fingerling salmon and trout of similar size were compared, and tests were run on fingerlings 2.3 to 3.0 inches in length and also on fingerlings 3.6 to 4.1 inches long. The fish were fed the Oregon moist pellet from 5 October to 20 December 1967. Daily feeding rates were kept below optimum and ranged from 1.8% to 3.6% of body weight. When trout and salmon below 3.3 inches were held together in the same raceway, the trout grew at a significantly faster rate; in other words steelhead trout were dominant over coho salmon in utilizing food from a limited supply. Above 3.3 inches the growth rate of the experimental trout was also greater than that of the salmon, although the difference was not significant at the 95% confidence level. Specific growth rates were dependent on the initial sizes of the fish.