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ABSTRACT
After restoration by whole-lake applications of liquid aluminum sulfate, Medical Lake, Washington, received a total planting of approximately 31,000 fingerling rainbow trout (Salmo gairdneri) from 1978 to 1980. Prior to treatment the lake had been unable to support game fish. Post-treatment improvement in water quality and zooplankton standing crops permitted good trout survival and growth. Daphnia pulex comprised over 90 percent of the trout diet for most age classes and dominated the biomass of the 0+ age class.
Size-selective predation was apparent for D. pulex 1.75 mm in length or larger. Intensive predation by trout appeared to be eliminating D. pulex as an available food source, which may jeopardize the effectiveness of the lake restoration as grazing on phytoplankton standing crop might diminish.
