Bioelectrical impedance analysis as a predictor of fish health and energy content in juvenile rainbow trout (Oncorhynchus mykiss)

Assessing the health of a fish is an essential part to aquaculture and fish research. This is traditionally done by measuring body content using bomb calorimetry or proximate composition analysis; however, both of these methods necessitate sacrificing the fish in order to obtain accurate data. This has led to research into novel non-lethal methods of analyzing fish tissue so as to determine the body composition and health condition of fish without sacrificing the animal. One such method is Bioelectrical Impedance Analysis (BIA). BIA is a quick, non-lethal procedure that can estimate the body content of fish by passing an electric current between two electrodes through the tissue of the fish. The focus of this study is to develop predictive equations non-lethally determine the water content, dry mass and energy content of juvenile rainbow trout (Oncorhynchus mykiss) and to determine whether the electrode position has an effect on the predictive capability of these equations. Three different sizes of juvenile rainbow trout were obtained: small (150mm length), medium (230mm length) and large (300mm length) and fasted over a period of two weeks. A third of each size group was sampled at the beginning of the fasting period and once every week after. Bioimpedance was measured along the dorsal, lateral and ventral axis of each fish. Tissue from each fish was obtained during sampling and analyzed afterward for energy content using bomb calorimetry. The results of this BIA study demonstrated a strong correlation between the BIA readings and total water content (r2=0.9170), dry mass (r2=0.9064) and energy content (r2=0.9149). The best predictive equations were developed from the dorsal BIA readings. These results indicate that BIA may be used as an accurate tool to non-lethally determine the energy content and health of rainbow trout in future studies