Timothy Copeland, Department of Fisheries and Wildlife
Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia
24061-0321; Voice 540-231-3329 FAX 540-231-7580 E-Mail tcopelan@vt.edu
Keywords: proximate composition, TOBEC, bluegill, regression
Proximate composition (ash, water, protein, and lipid content) is
commonly determined in studies of fish physiology, nutrition, and growth, but standard
techniques require sacrificing specimens. Here I investigate the field accuracy of a
method for nondestructive estimation of fish proximate composition previously used under
controlled conditions, total body electrical conductivity (TOBEC). Conductivity is
measured noninvasively within a detection chamber by changes in the magnetic field caused
by the tissues of the fish. I collected bluegills from two Virginia ponds. Water, lipid,
and protein content were measured using standard laboratory methods. I measured TOBEC of
each fish at pondside and again in the laboratory. Using laboratory TOBEC and whole-fish
variables, predictive regressions (R2 > 0.90) were developed from 63
randomly chosen bluegills and checked with the remaining 21 fish. Under controlled
conditions, TOBEC can be used to precisely and accurately predict proximate composition (
<6.4% mean error). Regressions developed from pondside TOBEC readings were similar in
accuracy (<7.1% mean error). TOBEC is a promising means to nondestructively estimate
fish proximate composition in the laboratory, hatchery, or field.
