Effective complete replacement of fish oil by linseed oil in diets for thick-lipped grey mullet (Chelon labrosus) juveniles reared at three environmental salinities

One of the major challenges for fish oil replacement by alternative oils is the limited capacity of marine fish species to convert 18C fatty acids into long-chain poly unsaturated fatty acids (LC-PUFA). Since salinity markedly affects this conversion capacity, euryhaline species, such as thick-lipped grey mullet (Chelon labrosus), may have a good potential to use diets without inclusion of fish oil. To test this hypothesis, thick-lipped grey mullet juveniles were fed two different diets based on fish oil (FO diet) or linseed oil (LO diet) at three different salinities: 46 ppt, 35 ppt, and 16 ppt. At the end of the trial, the biochemical and fatty acid composition of whole-body, liver, and muscle, as well as the relative expression of the genes codifying for the elongase Elovl5 and the desaturase Fads2 in liver, were determined. The results showed the good capacity of mullet juveniles to convert 18C fatty acids into LC-PUFA, which was enhanced by the replacement of FO by LO and the reduction of salinity to an isosmotic level (16 ppt). Besides, these juveniles efficiently used diets with complete replacement of FO by LO with growth performance, body composition, and LC-PUFA fatty acid profiles similar to those of fish fed FO, particularly when reared at 16 ppt.