Developing bioelectrical impedance analysis methods for small fish

Bioelectrical impedance analysis (BIA) is a tool that can produce nonlethal proximate composition estimates for fish. For many fishes year class strength is largely determined by survival through the first winter. Increased fat reserves of small fish result in improved winter survival and overall cohort success. BIA methods are established for estimating proximate composition of brook trout (Salvelinus fontinalis) ranging 110-285 mm but none have been developed for early life stages or adults of small-bodied forms. The objective of this study was to develop BIA methods that provide reliable percent based estimates of body composition for small fish. To achieve this objective brook trout ranging 48-115 mm total length had BIA measurements taken at seven locations using both subdermal needle and external rod electrodes. BIA models did an excellent job predicting percent dry weight of test data sets. Subdermal needles produced the best model but it was only slightly better than the best model developed using external rod electrodes. Using two electrode locations developed better models than when only one location was used. For small brook trout the DTVpre location should be used in conjunction with the DTL or DML locations when taking BIA measurements to produce the best results.