Figure 4: Structures of some ω3 polyunsaturated fatty acids present in marine samples. Hexadecatrienoic acid (16:3ω3), α-linolenic acid (ALA, 18:3ω3), octadecatetraenoic acid (OTA, 18:4ω3), eicosapentaenoic acid (EPA, 20:5ω3), ω3 docosapentaenoic acid (ω3DPA, 22:5ω3), and docosahexaenoic acid (DHA, 22:6ω3) are all related biochemically because of the location of the first double bond 3 carbons from the methyl end of the chain.