Assimilation Efficiency of Utah Sucker and Speckled Dace Feeding on Chironomidae Larvae at Different Temperatures

ASSIMILATION EFFICIENCY OF UTAH SUCKER AND SPECKLED DACE FEEDING ON CHIRONOMIDAE LARVAE AT DIFFERENT TEMPERATURES

N. D. HEYREND, K. C. DONNER, and C. V. Baxter

Stream Ecology Center, Department of Biological Sciences, Idaho State University, Pocatello, ID

Abstract

Assimilation efficiency is an important, yet often overlooked component of many studies in fish trophic ecology.  A common assumption in these studies is that assimilation efficiencies are constant despite growing evidence to the contrary.  Some studies have addressed variability in assimilation efficiency with respect to temperature however; our understanding of consumer-specific variation in assimilation efficiency is limited.  We examined assimilation efficiency of speckled dace and juvenile Utah sucker feeding on Chironomidae at 20 ± 3C and 12 ± 3C. We chose these as species representative of fish families (Cyprinidae and Catostomidae) that are ecological important in rivers of the western U.S. but whose assimilation efficiencies are poorly understood, and investigated their utilization of Chironomidae larvae because they are among the invertebrate prey most commonly consumed by these fishes.  Individuals of each species were held in 7.5 gallon aquaria and fed a diet of frozen Chironomidae larvae.  Feces were collected throughout the experiment assimilation efficiency was determined by using an indigenous marker technique.  Assimilation efficiency was highest in the 20C treatment containing Utah sucker and lowest in the 12C treatment containing dace.  For each species, assimilation efficiency was higher in the 20C treatment than the 12C treatment.  Higher assimilation efficiencies in Utah sucker may be attributed to longer gut lengths relative to speckled dace. Variability in assimilation efficiency associated with temperature can be important to account for in bioenergetic models.  Efficiencies estimated through this study may be useful in parameterizing bioenergetic models for these and related fishes.