Asian sea bass, Lates calcarifer

Lates calcarifer, commonly known as the Asian sea bass or barramundi, is an 16 interesting species that has great aquaculture potential in Asia including Malaysia and also 17 Australia. We have investigated essential fatty acid metabolism in this species, focusing on 18 the endogenous highly unsaturated fatty acid (HUFA) synthesis pathway using both 19 biochemical and molecular biological approaches. Fatty acyl desaturase (Fad) and elongase 20 (Elovl) cDNAs were cloned and functional characterization identified them as ∆6 Fad and 21 Elovl5 elongase enzymes, respectively. The ∆6 Fad was equally active towards 18:3n-3 and 22 18:2n-6, and Elovl5 exhibited elongation activity for C 18-20 and C 20-22 elongation and a trace of 23 C 22-24 activity. The tissue profile of gene expression for ∆6 fad and elovl5 genes, showed 24 brain to have the highest expression of both genes compared to all other tissues. The results of 25 tissue fatty acid analysis showed that the brain contained more docosahexaenoic acid (DHA, 26 22:6n-3) than flesh, liver and intestine. The HUFA synthesis activity in isolated hepatocytes 27 and enterocytes using [1-14 C]18:3n-3 as substrate was very low with the only desaturated 28 product detected being 18:4n-3. These findings indicate that L. calcarifer display an essential 29 fatty acid pattern similar to other marine fish in that they appear unable to synthesize HUFA 30 from C 18 substrates. High expression of ∆6 fad and elovl5 genes in brain may indicate a role 31 for these enzymes in maintaining high DHA levels in neural tissues through conversion of