Marine and freshwater fish oil varying in arachidonic, eicosapentaenoic and docosahexaenoic acids differ in their effects on organ lipids and fatty acids in growing rats.

Arachidonic acid [20:4(n-6)] and docosahexaenoic acid [22:6(n-3)] are important to normal neurodevelopment and visual function. Infants fed formula often have low blood lipid 20:4(n-6) and 22:6(n-3). Consumption of fish oils high in eicosapentaenoic acid [20:5(n-3)] and 22:6(n-3) with no 20:4(n-6) increases tissue 20:5(n-3) and 22:6(n-3) but decreases 20:4(n-6). Some freshwater fish oils contain higher 20:4(n-6) and lower 20:5(n-3) than usual marine fish oils, but their effects on tissue fatty acids are not well known. Therefore, the effects of feeding weaning rats 30 d with 12% (wt/wt) soybean oil [0.0% 20:4(n-6), 20:5(n-3) and 22:6(n-3)], 2% safflower oil with 10% marine fish oil [0.9% 20:4(n-6), 15.1% 20:5(n-3), 7.3% 22:6(n-3)] or 10% freshwater fish oil [3.3% 20:4(n-6), 5.9% 20:5(n-3), 8.0% 22:6(n-3)] on plasma, tissue and brain fatty acids was determined. Levels (g/100 g) of 20:4(n-6) were significantly higher and 20:5(n-3) lower in plasma, liver, kidney and brain of rats fed freshwater fish oil rather than marine fish oil. Marine fish oil, but not freshwater fish oil resulted in a higher brain 20:5(n-3) and 22:6(n-3), and lower 20:4(n-6) than soybean oil. Plasma and liver triglyceride concentrations were significantly lower in rats fed marine fish oil, but not in rats fed soybean oil when compared with those fed freshwater fish oil. The results indicate dietary 20:4(n-6) prevents the decline in plasma and tissue 20:4(n-6) caused by dietary 20:5(n-3) and/or 22:6(n-3). Oils with 20:4(n-6) may affect cholesterol and triglyceride metabolism differently than usual fish oils.