Body Condition Correlates with Instantaneous Growth in Stream-Dwelling Rainbow Trout and Arctic Grayling

Abstract

Understanding the growth response of fish to varying environmental and biological conditions is important for the management and conservation of populations and communities. However, obtaining growth data at time scales shorter than those provided by annual size-at-age relationships is costly and labor intensive and can be logistically impractical. We assessed the ability of a body condition index to serve as a proxy for individual instantaneous growth rates in two species of mostly subadult stream-dwelling salmonids in southwestern Alaska. We found that relative body condition, as measured by the residuals around a length–mass regression, was strongly correlated with direct measures of individual instantaneous growth (day⁻¹) from mark–recapture data. Further, body condition was significantly correlated with growth accumulated over a period of roughly 2–10 weeks in both Rainbow Trout Oncorhynchus mykiss and Arctic Grayling Thymallus arcticus, while the relationship was typically weaker for time periods of less than 2 weeks and greater than 1 year. Despite the limitations of using body condition indices to infer the physiological status of individuals, our results demonstrate that, when applied judiciously, body condition can be used as a surrogate for recent individual instantaneous growth rate.

Received June 30, 2012; accepted January 9, 2013

ACKNOWLEDGMENTS

This is a contribution of the Alaska Salmon Program of the University of Washington, with funding provided by the National Science Foundation through a graduate research fellowship to K.T.B. and grants from the Biocomplexity and Dynamics of Coupled Nature and Human Systems programs, and from the Gordon and Betty Moore Foundation. We thank the staff of the Wood-Tikchik State Park for supporting our research and the numerous individuals who assisted with field work including J. Moore, M. Scheuerell, C. Ruff, P. Lisi, M. Consoer, M. Kimble, H. Stapleton, K. Omori, T. Edwards, K. Jankowski, A. Hilborn, R. Kelly, L. Payne, G. Holtgrieve, E. Davis, and J. Armstrong. T. Essington and K. Broms aided in data analysis. A. Rypel and one anonymous reviewer provided valuable improvements to the manuscript.