Michigan Department of Natural Resources
Institute for Fisheries Research Report No.1761, 1969

Effects of Gill Lice (Salmincola edwardsii) on Brook Trout (Salvelinus fontinalis) in Lakes

L. N. Allison and W. C. Latta

      Abstract.-Six small lakes (3-10 acres) stocked annually with brook trout at the Pigeon River Fisheries Research Station, Vanderbilt, Michigan, have well established populations of S. edwardsii. This parasite was considered a possible cause of natural mortality of fish in these lakes. Objectives were to measure parasitism of gill lice on brook trout in relation to condition and rate of natural mortality of fish, and possibly identify factors influencing development of gill lice populations. Annual trout population estimates were made. Monthly samples of fish were taken from each lake January through December, 1964. Gill lice on each trout were counted and classified as to stage of development. Reproduction continued throughout the year. No relationship was found between parasitism and condition and rate of natural mortality of brook trout. Development of gill lice populations was not influenced by a summer decrease in volume of water with suitable temperature and oxygen characteristics for trout. Degree of infestation was most influenced by degree of infestation of older fish in each lake. In four lakes gill lice populations developed exponentially, and the rate of increase was inversely related to initial number of gill lice on fish.