Food relations and production of cutthroat trout, Salmo clarki clarki Richardson, in an experimental stream

Abstract

Production, food consumption and food habits by groups of small, mixed and large sizes of cutthroat trout were studied in enriched and unenriched sections of the Berry Creek Experimental Stream, Oregon State University. Continuous introduction of sucrose and urea to portions of the stream resulted in heavy growth of Sphaerotilus natans which supported large biomasses of benthic insects. Production was estimated from monthly changes of biomass. Measurements of growth rates of experimental fish and the relationship between rates of growth and rates of food consumption of fish held in aquaria made estimates of food consumption by the stream fish possible. Analyses were made of the stomach contents of trout removed monthly from the experimental sections. The seasonal contribution to trout food consumption by the important food groups was estimated. Measurements of benthic biomass showed that insects especially midge larvae, benefited greatly from the Sphaerotilus in the enriched sections but organic drift did not increase markedly as a result of enrichment. In both enriched and unenriched sections trout production and food consumption values were highest for small trout, intermediate for mixed sizes and lowest for large trout. Production and food consumption by all size groups of trout increased greatly as a result of enrichment.