Season variation in nutrient composition of Alaskan walleye pollock

Abstract

A popular hypothesis for the noted steady decline in the population of Steller sea lions, Eumetopias jubatus (Schreber, 1776), in the regions from Prince William Sound through the Aleutian Islands relates to their nutritional status. Sea lion diets appear to have shifted from primarily small schooling fatty fishes to low-fat fish such as walleye pollock, Theragra chalcogramma (Pallas, 1814). We examined the seasonal changes in proximate nutrients of pollock collected in the Bering Sea. Mean energy density (dry mass) of pollock peaked in October then declined and remained low throughout winter. Energy recovery occurred in the summer months with strong recovery observed in female fish caught in July. Contrary to whole fish carcass energy contents, both total protein and moisture contents were at their highest levels in winter (January) when total crude lipid content was at its lowest (p < 0.05). This trend gradually declined to its lowest levels in the fall when lipid content was high. The decline in total lipids during winter seasons appeared to parallel gonad development during the prespawning period. Sex differences in energy densities were not found. Proximate analysis data for moisture, protein, ash, and lipid content also did not show any significant variation between males and females. Protein digestibility of pollock was higher (p < 0.05) in the summer than in the spring, but not different for winter or fall. We concluded that the nutrient content of walleye pollock may have some impact on the Steller sea lions that feed on them, particularly the energetic value that appears to be low during important feeding periods for this marine mammal.

Influence of dietary conjugated linoleic acid on growth, fatty acid composition and hepatic lipogenesis in large yellow croaker (Pseudosciaena crocea R.)

“…Fatty acids were methylated with boron trifluoride (BF 3 ) in methanol (Kitts et al, 2004). The fatty acid methyl esters (FAME) were analyzed by gas chromatograph (Agilent 6890, USA) equipped with flame ionization detector and an auto injector (Agilent 7683, USA).…”

Synergistic Effect of Nickel and Mercury on Fatty Acid Composition in the Muscle of Fish Lates calcarifer

“…The fatty acid composition might be related to the changes in nutritional habits of the fish. Kitts et al (2004) reported that the fatty acid composition and lipid contents of fish were affected by the species, sex, age, water temperature, degree of pollution, nutritional condition, seasonal variation and fish origin. The nutritional benefits of fish are mainly due to the content of high quality protein and high content of two kinds of ω-3 polyunsaturated fatty acids.…”

Vitamin E Profiles and Triacylglycerol Molecular Species of Colored Rice Bran Cultivars at Different Degree of Milling

“…Methyl pentadecanoate (10-100 g) from a standard solution (5 mg/ml) was added to each tube as the internal standard, except that pentadecane (10 g) was used as the internal standard for hydrocarbons analysis. FAME was prepared by heating with silica gel for 30 min at 80 ºC in BF 3 /methanol (Kitts et al, 2004). The FAME was quantified by gas chromatography (GC, 14B GC Shimadzu) equipped with a hydrogen flame ionization detector (FID) at 350 C and a polar capillary column (ULBO HE-SS-10 for FAME, fused silica WCOT [no.…”