Michigan Department of Conservation
Institute for Fisheries Research Report No.1742, 1967
Competition Between Coho Salmon and Rainbow Trout in the Laboratory
Percy W. Laarman
Abstract.-Competition between coho salmon and rainbow trout was studied by comparing growth of the two species when held together in a laboratory raceway. Fish (5 inches long) were fed the Oregon moist pellet for 28 days at the daily rate of 2.5% of body weight. The rainbow controls, rainbow experimentals, and coho controls increased in weight an average of 8.1, 8.4 and 4.1 grams respectively. Coho experimentals lost an average of 1 gram per fish. The conclusion is that rainbow trout were dominant over coho salmon in getting food, with the result that the salmon made no growth. The introduction of coho salmon, Oncorhynchus kisutch (walbaum), into Michigan waters presents many questions and problems for fish management. One of these problem areas is the competition for food that may exist between fingerling coho salmon and native trout in streams. The purpose of this experiment was to investigate possible competition between coho salmon and rainbow trout, Salmo gairdneri Richardson, by comparing growth of the two species held under controlled conditions. Kalleberg (1958) reported that brown trout parr, Salmo trutta L., were more aggressive and grew faster than juvenile Atlantic salmon, Salmo salar L., on natural foods available in a stream tank. Le Cren (1965) found that trout fry dominated salmon fry (species not given) in a small experiment which involved planting different proportions of salmon and trout eggs in the same section of stream.