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

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 degrees C-30 degrees C), postprandial state (2-72 h), and time out of the water (2 h) on five impedance parameters (resistance at infinite frequency [R-inf], resistance at zero frequency [R-0], resistance at 50 kHz [R-50], phase angle at 50 kHz [PhA(50)], and intracellular resistance [R-i]) using a bioimpedance spectroscopy device. Technical reproducibility of measurements and interanimal variability were also assessed. We found an inverse exponential relationship between change in environmental temperature and impedance parameters R-inf, R-0, and R-50. Postprandial state significantly increased R-inf and R-i 72 h after feeding. BIA measurements were reproducible within individual juvenile green turtles at temperatures from 20 degrees C to 30 degrees 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 environmental temperatures close to their preferred thermal range. We propose a standardized protocol of measurement conditions to facilitate laboratory and field use of BIA for body composition assessment studies in turtles.