71 



Abstract.— We evaluated the use of to- 

 tal body electrical conductivity ( TOBEC ) 

 for determination of whole-body water 

 content of yellow perch, Perca flavescens, 

 and alewife. A/osa pseudoharengus. We 

 used multiple linear regression with 

 backwards stepwise elimination to test 

 the capability of TOBEC values, wet 

 weight, and total length in predicting 

 whole-body water content of yellow 

 perch and alewife. We found that wet 

 weight was the best predictor of whole- 

 body water content. The inclusion of 

 TOBEC values in multiple linear re- 

 gressions did not improve the predic- 

 tive capability of wet weight over 

 simple linear regressions that used wet 

 weight alone (r- increased by only 

 0.00002 to 0.0005). We reanalyzed the 

 data from three previous studies that 

 used TOBEC to evaluate the tissue 

 composition of fish. Again we found 

 that the inclusion of TOBEC values in 

 regression functions with wet weight as 

 the other independent variable did not 

 substantially improve the predictive 

 capability of functions that used wet 

 weight alone (r'^ increased by only 

 0.00003 to 0.0007). 



Evaluation of total-body electrical conductivity 

 to estimate whole-body water content of 

 yellow perch, Perca flavescens^ and alewife, 

 Alosa pseudoharengus* 



Brian F. Lantry 

 Donald J. Stewart 



State University of New York 



College of Environmental Science and Forestry 



1 Forestry Drive, Syracuse, New York 13210 



Present address (For B F Lantry): New York State Department of Environmental Conservation 



Cape Vincent Fisheries Station 

 P.O. Box 292, Cape Vincent, New York 13618 



E-mail address (for B F Lantry) blantryfflimcnetnet 



Peter S. Rand 



North Carolina State University 



1 Clark Labs, Raleigh, North Carolina 27695 



Edward L. Mills 



Cornell University Biological Field Station 



900 Shackelton Point Road, Bridgeport, New York 13030 



Manuscript accepted 14 April 1998. 

 Fish. Bull. 97:71-79(1999). 



Attempts to construct energy bud- 

 gets for many important fish spe- 

 cies are often hampered by the lack 

 of data on their energy density. Fur- 

 ther, the study of energy flow in 

 aquatic communities is complicated 

 by seasonal variation of the energy 

 density within organisms and rela- 

 tive differences in energy content of 

 predator and prey (Craig, 1977; 

 Stewart et al, 1983; Stewart and 

 Binkowski, 1986; Rand et al., 1994). 

 The shortage of useful data is due 

 in part to the difficulty of determin- 

 ing the energy content of large num- 

 bers of individuals. Estimation of 

 fish energy density has been sim- 

 plified with development of relation- 

 ships, based on calorimetric analy- 

 sis, between percentage dry weight 

 (lOOxfdry weight/wet weight)) and 

 wet weight energy density (Stewart 

 and Binkowski, 1986; Rand et al., 

 1994; Hartman and Brandt, 1995; 

 Lantry, 1997). The measurement of 

 dry weights on substantial numbers 

 of large individual fish, however, 

 can be problematic, because they 



require considerable time to dry, use 

 large amounts of oven space, and 

 may require time-consuming sec- 

 tioning or grinding procedures. 



Measurement of total body electri- 

 cal conductivity (TOBEC) has been 

 presented in the literature as a reli- 

 able alternative to the sacrifice of or- 

 ganisms to evaluate tissue composi- 

 tion. Lipid content and lean body 

 mass have been accurately estimated 

 by measuring TOBEC in humans, 

 swine, rats and birds (Domermuth et 

 al., 1976; Bracco et al., 1983; Presta 

 et al. 1983; Keim et al, 1988; Wals- 

 berg, 1988; Castro et al., 1990). 

 TOBEC has recently been used for 

 the estimation of body composition of 

 three fish species: sunshine bass (a 

 white bass [Morone chrysops] x 

 striped bass [Morone saxatilis] hy- 

 brid. Brown et al., 1993); red drum 

 (Sciaenops ocellatus, Bai et al., 1994); 

 and channel catfish (Ictalurus punc- 

 tatus, Jaramillo et al., 1994). 



' Contribution 179 of Cornell University 

 Biological Field Station, Bridgeport, New 

 York, NY 13030. 



