Effects of dietary α‐linolenic acid/linoleic acid ratio on growth performance, tissue fatty acid profile, serum metabolites and Δ6 fad and elovl5 gene expression in silver barb (Puntius gonionotus)

Abstract BACKGROUND Silver barb ( Puntius gonionotus ) is a medium‐sized carp that is promising for freshwater aquaculture in Asia. This study's aim was to investigate the ideal dietary α‐linolenic acid (ALA): linoleic acid (LA) ratio for maximizing long‐chain polyunsaturated fatty acid (LC‐PUFA) synthesis and their deposition in the muscle of silver barb, as that of fish oil based control diet. RESULT Fish (with an initial body weight of 11.07 ± 0.12 g) were fed for 60 days with five experimental iso‐proteinous, iso‐lipidic, and iso‐caloric diets, supplemented with linseed oil and peanut oil at varying levels to obtain ALA:LA ratios of 0.35, 0.51, 0.91, 2.04, 2.66. A control diet was prepared by supplementing fish oil. The dietary ALA:LA ratio did not influence the growth performance of fish. With increased dietary ALA:LA ratios, LA content decreased and ALA content increased in the muscle and liver of silver barb. The n‐3 LC‐PUFA level in muscle and liver was not influenced by feeding different ratios of ALA:LA, whereas n‐6 LC‐PUFA was decreased in the muscle and increased in the liver with increased dietary ALA:LA ratios. Increasing dietary ALA:LA ratio increased the Δ6fad and elovl5 mRNA expression in the liver, muscle, brain, and intestinal tissues of silver barbs. CONCLUSION Silver barb possess the ability to elongate and desaturate ALA and LA to their end products EPA and DHA. The highest level expression of Δ6 fad and elovl5 mRNA at the dietary ALA:LA ratio of 2.66 suggests greater affinity of these enzymes towards ALA than LA in silver barb. © 2019 Society of Chemical Industry