Lipid and Moisture Content Modeling of Amphidromous Dolly Varden Using Bioelectrical Impedance Analysis

Abstract

The physiological well-being or condition of fish is most commonly estimated from aspects of individual morphology. However, these metrics may be only weakly correlated with nutritional reserves stored as lipid, the primary form of accumulated energy in fish. We constructed and evaluated bioelectrical impedance analysis (BIA) models as an alternative method of assessing condition in amphidromous Dolly Varden Salvelinus malma collected from nearshore estuarine and lotic habitats of the Alaskan Arctic. Data on electrical resistance and reactance were collected from the lateral and ventral surfaces of 192 fish, and whole-body percent lipid and moisture content were determined using standard laboratory methods. Significant inverse relationships between temperature and resistance and reactance prompted the standardization of these data to a constant temperature using corrective equations developed herein. No significant differences in resistance or reactance were detected among spawning and nonspawning females after accounting for covariates, suggesting that electrical pathways do not intersect the gonads. Best-fit BIA models incorporating electrical variables calculated from the lateral and ventral surfaces produced the strongest associations between observed and model-predicted estimates of proximate content. These models explained between 6% and 20% more of the variability in laboratory-derived estimates of proximate content than models developed from single-surface BIA data and 32% more than models containing only length and weight data. While additional research is required to address the potential effects of methodological variation, bioelectrical impedance analysis shows promise as a way to provide high-quality, minimally invasive estimates of Dolly Varden lipid or moisture content in the field with only small increases in handling time.

Received June 17, 2013; accepted December 3, 2013

ACKNOWLEDGMENTS

We thank Mark Nelson, John Richard, and Dave Sowards for assistance in capturing fish in the field and Peter Bechtel, Lara Hortsmann-Dehn, and Matthew Wooller for the use of their laboratory facilities. Scientific sampling was conducted under the authority of Alaska Department of Fish and Game fishery resource permits SF2010-088, SF2011-046, and SF2012-265. Funding for this study was provided by the U.S. Fish and Wildlife Service, Arctic National Wildlife Refuge and the Fairbanks Fisheries Resource Office. The care and handling of all fish included in this study was in accordance with approved protocols of the University of Alaska–Fairbanks’ Institutional Animal Care and Use Committee assurance 175440-3. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.