Omega-3 fatty acid pathway. The human omega-3 fatty acid metabolism pathway is composed of 12 enzymes. The enzymes colored in red are not found in fish. The three enzymes in yellow are in the gene families found in fish, but the presence of these specific enzymes is not clear. This shows that fish lack enzymes to convert the intermediate metabolites, which are the source of omega-3 fatty acids important to human health. The common omega-3 fatty acid variants are in red font.