fish oil fish oil fish oil is oil derived from the tissues of oily fish. fish oils contain the omega-3 fatty acids eicosapentaenoic acid (epa) and docosahexaenoic acid (dha), precursors of certain eicosanoids that are known to reduce inflammation in the body and improve hypertriglyceridemia. there has been a great deal of controversy in recent years about the role of fish oil in cardiovascular disease, with recent meta-analyses reaching different conclusions about its potential impact. the most promising evidence supports supplementation for prevention of cardiac death. for omegaven, see fish oil (medical use).