Total Body Electrical Conductivity for Nondestructive Measurement of Body Composition of Red Drum
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A. rapid and nondestructive method for predicting body composition by measuring total body electrical conductivity (TOBEC) was evaluated with red drum (Sciaenops ocellatus). This noninvasive technique consisted of placing fasted (48 h) and anesthetized fish within a low- frequency electromagnetic field and measuring the TOBEC. Body composition then was predicted on the principle that body fat and fat-free mass differ in electrical properties. Relationships between TOBEC and body composition were examined with 40 red drums ranging from 10 to 138 g. There were significant (P < 0.0001) positive linear correlations between TOBEC values and measured body components; correlation coefficients for body weight, body water, protein, lipid, lean body mass, and ash were 0.960, 0.967, 0.947, 0.809, 0.959, and 0.799, respectively. Repeated TOBEC measurements also were made on fish that were fed, fasted (48 h), frozen, and thawed to determine the effects of these states on TOBEC. Average TOBEC values for fish in the fed and frozen states were significantly (P < 0.05) higher than those obtained in the fasted or thawed states; furthermore, the thawed state resulted in the lowest values. Models including weight, length, and TOBEC variables provided adequate estimates of body composition for live, individual red drums that ranged widely in body weight. However, because TOBEC measurements were influenced by physical and physiological conditions of the fish, these factors should be standardized. 1994 by the American Fisheries Society.
