In this paper our quantitative analytical system for fatty acids in foods (Hywönen ct al., J. Food Comp. Anal 6, 24-40, 1993) was applied to 33 fresh and processed fish. fish liver, and roe commodities sampled with our conventional system for average composition in a spring season from the Helsinki area. On the basis of total fatty acids, triacylglycerol (TAG) equivalents were calculated for the quantitation of net fat. Seven nutritional attributes for fish fat are also presented based on the fatty acid composition and physiological functions of fatty acids. The analytical system was readily applicable to fish and fish products and at most 34 different fatty acids were present at (0.1 \mathrm{wt} %) or more. I.inear regression analysis of the crude fat (CF) ( (\mathrm{g} / 100 \mathrm{~g}) of the fresh or frozen fish) determined with a chloroform-methanol (1:1) solvent extraction and the net fat value as TAG equivalents ((\mathrm{g} / 100 \mathrm{~g})) gave the equation (\mathrm{CF}=1.09 \mathrm{TAG}+1.79\left(R^{2}=0.988\right)). The equation demonstrates the risk for overestimation of the fatty acid contents, if the determination is based on analysis of relative fatty acid composition of the crude fat instead of direct quantitative fatty acid analysis. The net fat content of the various species of fresh fish varied from 0.7 to (8.9 \mathrm{~g}) per (100 \mathrm{~g}) of edible portion of fish. Liver and roe samples were about (6 \mathrm{~g}) and processed products from 0.2 to (13.5 \mathrm{~g}) of TAG equivalents. The proportion of the saturated fatty acids in fresh fish varied from 20 to (28 \mathrm{wt}^{\mathrm{w} %}), the range of the (\mathrm{C} 12-\mathrm{C} 16) variable being 17 to (27 \mathrm{wt} %). The stearic acid content was low (1.5-4.9 wt%). The cis monoenic fatty acid content in the fish fat varied greatly, from 16 to (51 \mathrm{wt} %). The range of the total of all cis di- and polyenes was 25 to (61 \mathrm{wt} %). The most characteristic nutritional attribute of fish fat, (n-3) fatty acids, ranged from 24 to (58 \mathrm{wt} %). The influence of vegetable oils/margarine on the nutritional attributes of fish fat was evident in such items as tuna and sardines in oil and frozen prefried fish sticks ("fish fingers"). In general the (\mathrm{n}) (3 / \mathrm{n}-6) ratio of the fish species analyzed proved to be large, although significant differences (2.831.4) were found between species in this respect. A clear tendency toward higher (n-3 / n-6) ratios was determined in the fish species with lower net fat contents. The data support the recommendation 10 apply a quantitative fatty acid analysis also for fish and fish products for quantifying the net fat as TAG equivalents as well as for quantifying various nutritional attributes of the fish fats. ci 1994 Academic Press, Inc.