Comparison of chloroform-methanol-extracted and solvent-free triglyceride determinations in four fish species

Lipids, including triglycerides, are important variables in fish bioenergetics and can be used to estimate overall fish condition. Triglycerides are the major energy storage form in fish and therefore are a more ecologically and physiologically relevant measure of bioenergetics than total lipids. Chloroform-methanol-extracted total body lipids (Bligh and Dyer) and total body triglycerides determined in chloroform-methanol extracts and unextracted whole-body fractions were measured in four fish species: northern pike Esox lucius, burbot Lota lota, slimy sculpin Cottus cognatus, and spottail shiners Notropis hudsonius. Determinations of total body lipids were consistently greater than those of total body triglycerides when measured in the same solvent-extracted fraction, although both measures followed similar trends. In an effort to eliminate the need for extraction with organic solvents, we compared the performance of an enzyme-based triglyceride assay in both the solvent-extracted fraction and a whole-body unextracted homogenate for each fish. The chloroform-methanol-extracted triglyceride values were consistently lower than triglycerides measured in the unextracted whole-body homogenate. In addition, comparison of triglyceride measurements revealed limitations to the solvent extraction and subsequent triglyceride determinations in lean fish. Thus, in addition to being simple, rapid, and not requiring organic solvents, determination of triglycerides in an unextracted whole-fish homogenate may be a useful alternative to chloroform-methanol-based methods of lipid extraction and subsequent triglyceride measurement.