A Standardized Protocol for Measuring Bioelectrical Impedance in Green Turtles (Chelonia mydas)

Abstract

Bioelectrical impedance analysis (BIA) is gaining popularity in wildlife studies as a portable technology for immediate and nondestructive predictions of body composition components, such as fat-free and fat masses. Successful application of BIA for field-based research requires the identification and control of potential sources of error, as well as the creation of and adherence to a standardized protocol for measurement. The aim of our study was to determine sources of error and to provide a standardization protocol to improve measurement precision of BIA on juvenile green turtles (Chelonia mydas; n = 35). We assessed the effects of altered environmental temperature (20°C–30°C), postprandial state (2–72 h), and time out of the water (2 h) on five impedance parameters (resistance at infinite frequency [Rinf], resistance at zero frequency [R0], resistance at 50 kHz [R50], phase angle at 50 kHz [PhA50], and intracellular resistance [Ri]) using a bioimpedance spectroscopy device. Technical reproducibility of measurements and interanimal variabilitywere also assessed. We found an inverse exponential relationship between change in environmental tem-perature and impedance parameters Rinf, R0,andR50. Postprandial state significantly increased Rinf and Ri 72 h after feeding. BIA measurements were reproducible within individual juvenile green turtles at temperatures from 20°Cto30°C. Significant variation in impedance values was found between animals at all temperatures, sampling times, and postprandial states, but the relative differences (%) were small in magnitude. Our study suggests that measurement precision is improved by measuring animals at consistent environmentaltemperaturesclosetotheir preferredthermalrange. We propose a standardized protocolof measurement conditionsto facilitate laboratory and field use of BIA for body composition assessment studies in turtles.