Pacific herring (Clupea pallasi).

Proximate analysis is used to estimate the relative amounts of protein, lipid, water, ash and carbohydrate in an organism. Protein, lipid, and carbohydrate each contribute to the total energy content of an organism while water and ash only contribute mass. Consequently, the total energy content of a specimen can be reconstructed from its proximate composition. Energy content is frequently used as an expression of a fish’s condition or health status. However, the relative contributions of lipid, protein, and carbohydrate to a fish’s total energy vary in response to specific life history demands.

In the Nutritional Ecology Laboratory, we examine proximate composition of marine forage species to understand the interplay between the constraints imposed by the environment and life history strategy on observed energy flux.

Seasonal Lipid Content of Pacific Herring
	Body composition of planktivorous forage species fluctuates significantly at high latitudes as a result of seasonal periods of food availability and spawning expenditures. The seasonal whole-body lipid content of Pacific herring (Clupea pallasi) (mean ± 95% confidence interval) expressed on a wet-mass basis is depicted, where vertical dashed lines indicate spawning periods.

Analysis of Energy Content: Bomb Calorimetry vs. Calculation
Energy content determined directly from bomb calorimetry and indirectly calculated using calorific equivalents for protein and energy yield similar results. In the Nutrition Ecology Laboratory, we regularly estimate energy content via calculation because of the powerful information incorporated in proximate composition data.

Energy Allometry of Juvenile Capelin
Analysis of the allometries between energy and length allow us to examine energy allocation strategies of marine species. Here we show log-log relationships between body length and energy content derived from lipid and protein in juvenile capelin. Comparison of lipid energy allocation lines for December and March shows a larger decrease in lipid for age-1 capelin than for age-0 capelin. Conversely, comparison of the protein energy line indicates that age-0 capelin lose more protein energy than age-1 capelin between December and March. This loss in structure for age-0 capelin suggests that winter mortality may be an important component to capelin recruitment.
	Life stages of capelin (Mallotus vilosus).

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