Fatty acid bioconversion capacity of rainbow trout (Oncorhynchus mykiss) : temperature and nutritional modulation

The production of fish rich in omega-3 long chain polyunsaturated fatty acids (n-3 LC-PUFA) has become a challenge considering the necessary replacement of the finite and expensive fish oil used in fish feed by alternative, often plant-derived, oils and the increased temperature induced by global warming. Interestingly, rainbow trout (Oncorhynchus mykiss) possess a relatively high capacity to synthesise n-3 LC-PUFA from α-linolenic acid (ALA). In the present work, impacts of increased water temperature, fish n-3 polyunsaturated fatty acids (PUFA) depletion and lignans on the fatty acid bioconversion capacity of rainbow trout were investigated via in vivo and in vitro approaches. Firstly, fish were subjected to increased temperature and fed a fish oil or ALA-rich linseed oil diet. The increased temperature reduced the fatty acid bioconversion capacity of trout fed a linseed oil diet but only slightly affected their n-3 LC-PUFA content. In contrast, the replacement of fish oil by linseed oil induced an increased bioconversion capacity but highly decreased the fish n-3 LC-PUFA content. Secondly, the fatty acid bioconversion capacity of rainbow trout was evaluated with fish previously depleted in n-3 PUFA. The study demonstrated that the basal high bioconversion capacity of rainbow trout was not modulated by fish n-3 PUFA depletion. Finally, lignans from sesame and linseed oils were evaluated as enzymatic modulators of the n-3 LC-PUFA biosynthesis pathway through an in vitro approach with the rainbow trout liver cell line RTL-W1 enriched in ALA. The sesame seed lignans reduced the fatty acid bioconversion of RTL-W1 cells while no effect of linseed lignans was reported. This work provides useful information in the search for feeding strategies aiming at providing consumers with n-3 LC-PUFA-rich fish and on the negative impact of global warming on aquaculture.