In vivo measurement of total body lipid content of common carp (Cyprinus carpio L.) by electrical conductivity

A non-destructive method to predict the total lipid content and the lean body mass (LBM) was evaluated by measuring the total body electrical conductivity (TOBEC) with common carp. This technique is based on the principle that body fat and fat-free mass differ in electric properties which can be measured in a low-frequency electromagnetic field. Experimental fish with average body weight of 1225±298 g originated from a commercial stock. Fish were slaughtered immediately after the measurements and homogenized samples were taken from the grinded whole-body. The fat content of the homogenates was analysed using Soxhlet extraction after hydrochloric acid digestion. The weight of lean body mass (LBM) was calculated as the difference between the live weight and the weight of fat determined. The TOBEC method provided very precise estimation of lean body mass (R2=0.99). Total body lipid content (in gram) can also be predicted from the E value and live weight with adequate accuracy (R2=0.66) in the size range of 706 – 1989 g in common carp. The predictibility of the crude fat content (in %) was moderate (R2=0.37) in the present investigation. It could not be increased significantly by including other body measurements as standard lenght, height and circumference. Fat content of table-sized, sexually matured common carp can be estimated at a precision level that may be adequate only if high selection pressure has to be applied in a breeding program.