In vertebrates, the essential fatty acids (FA) that satisfy the dietary requirements for a given species depend upon its desaturation and elongation capabilities to convert the C18 polyunsaturated fatty acids (PUFA), namely linoleic acid (LA, 18:2n-6) and α-linolenic acid (ALA, 18:3n–3), into the biologically active long-chain (C20–24) polyunsaturated fatty acids (LC-PUFA), including arachidonic acid (ARA, 20:4n-6), eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3). Recent studies have established that tambaqui (Colossoma macropomum), an important aquaculture-produced species in Brazil, is a herbivorous fish that can fulfil its essential FA requirements with dietary provision C18 PUFA LA and ALA, although the molecular mechanisms underpinning such ability remained unclear. The present study aimed at cloning and functionally characterizing genes encoding key desaturase and elongase enzymes, namely fads2, elovl5 and elovl2, involved in the LC-PUFA biosynthetic pathways in tambaqui. First, a fads2-like desaturase was isolated from tambaqui. When expressed in yeast, the tambaqui Fads2 showed Δ6, Δ5 and Δ8 desaturase capacities within the same enzyme, enabling all desaturation reactions required for ARA, EPA and DHA biosynthesis. Moreover, tambaqui possesses two elongases that are bona fide orthologs of elovl5 and elovl2. Their functional characterization confirmed that they can operate towards a variety of PUFA substrates with chain lengths ranging from 18 to 22 carbons. Overall our results provide compelling evidence that demonstrates that all the desaturase and elongase activities required to convert LA and ALA into ARA, EPA and DHA are present in tambaqui within the three genes studied herein, i.e. fads2, elovl5 and elovl2. Display omitted •Tambaqui Fads2 has Δ6, Δ5 and Δ8 desaturase capacities within the same enzyme.•Tambaqui possess both Elovl5 and Elovl2 enzymes enabling elongation of C18–22 PUFA substrates.•Tambaqui has desaturase and elongase activities required to biosynthesize ARA, EPA and DHA from dietary C18 precursors.