High-throughput determination of total lipids from North Pacific marine fishes via the sulfo-phospho-vanillin microplate assay

Total lipid content is a valuable indicator of fish health, prey quality, survival potential, stock health, and ecosystem status. Here, we demonstrate an accurate method for measuring total lipids in fish tissues using the spectrophotometric sulfo-phospho-vanillin (SPV) assay, adapted to a 96-well plate format. Samples of dried homogenate were cross-analyzed via the SPV assay and standard gravimetric lipid analysis. Initial measurements of whole fish homogenates analyzed include Pacific herring (Clupea pallasii), Pacific cod (Gadus macrocephalus), walleye pollock (G. chalcogrammus), Pacific capelin (Mallotus villosus), Chinook (Oncorhynchus tshawytscha), and coho (O. kisutch) salmon. Samples of muscle tissue were analyzed from Chinook, pink (O. gorbuscha), sockeye (O. nerka), and chum (O. keta) salmon. All SPV measurements were calibrated using menhaden oil. The mean absolute and relative difference between gravimetric and SPV analysis was 0.5 and ~ 16.4%, respectively (n = 121). To improve the accuracy of SPV assay results, linear calibration models specific to taxa and tissue matrix type were developed, enabling calculation of corrected SPV assay values. The accuracy of using these calibration models was tested by analyzing additional fish samples (n = 16). The results of the corrected SPV assay were not statistically different (p > 0.05) from gravimetric analysis for any samples measured, and the mean absolute and relative difference between the two assays improved to 0.2% and 4.6%, respectively. The SPV assay provides a rapid (2 h), high-throughput (25 samples processed in triplicate), precise (interassay coefficient of variation = 5.6%), and accurate method for quantifying the total lipid content of homogenized fish tissue.