Lipids have several functions within an organism, ranging from the primary form for energy storage to vital structural components in cell membranes. If we are interested in total energy for a prey, then a proximate composition analysis will be the most efficient way to get an estimate of the total energy content. If however, we want to know the energy being stored for later use in the winter, then lipid class analysis is needed to separate out the different forms of lipids so that the partitioning of the different classes can be determined. The partitioning between classes changes significantly between fish that are growing rapidly or storing energy, those that are fasting, and those that are moving energy into their reproductive products.

In the Nutritional Ecology Laboratory, we use lipid class analysis to partition lipids into their functional classes, including storage and structural lipids, and metabolic intermediates. Quantification of these functional groups allows us to examine how marine species metabolize lipids. Additionally, we have found lipid class analysis to be a significant improvement on other methods of assessing an organism's condition, such as the more course indices using length to mass ratios.
 

	Seasonal Energy Allocation of Walleye Pollock
			By examining the lipid composition of young-of-the-year pollock, we can infer the rapid turnover of lipid in September by noting the relatively low amounts of storage lipid and high amounts of metabolic intermediates. In contrast, we observe relatively large amounts of storage lipid in December when food supplies are diminished.

Contact
Ron Heintz
Auke Bay Laboratories
Alaska Fisheries Science Center, NOAA Fisheries

Ted Stevens Marine Research Institute
17109 Pt Lena Loop Rd
Juneau AK 99801
(907) 789-6058
Ron.Heintz@noaa.gov