Use of Bioelectric Impedance Analysis to Assess Total-Body Condition and Predict Energy Density in Juvenile Atlantic Croaker
2012
Garner, S. B. | van der Ham, J. L. | Boswell, K. M. | Cowan, J. H.
Bioelectric impedance analysis (BIA) uses the conductive properties of biological tissues to provide whole-body resistance (R) and reactance (X c) data through direct measurements of intracellular and extracellular water content. The application of BIA to fish remains relatively novel, and the relationship between condition and impedance is not fully understood. We sought to test the efficacy of BIA in assessing total-body condition and energy content in juvenile fish. We present results from a laboratory tank experiment using juvenile Atlantic croaker Micropogonias undulatus to investigate the BIA-condition relationship and compare BIA with traditional condition measures (i.e., relative condition and energy-content analysis). Atlantic croaker were held in large recirculation tanks and subjected to either a starvation or ad libitum feeding treatment for 45 d. Relative condition, energy content, phase angle, and the composition index all showed significant differences between treatments. However, trends observed in the BIA-derived condition measures (phase angle and the composition index) displayed contradictory results. When regressed against energy content, phase angle yielded consistently lower r ² values than relative condition, while both were much lower than literature-derived r ² values for predictive equations of proximate components. Two explanations are possible for the weak relationships observed among BIA measures in this experiment: (1) relatively high-metabolic rates and low energy storage capacities of juvenile fish may have disrupted normal impedance relationships, and (2) an electrode array placed in muscle tissue may not have detected compositional changes if the primary centers for fat storage and mobilization occurred in the liver or viscera.
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