"Fish are the major dietary source for humans of n-3 highly unsaturated fatty acids (HUFA) with important roles in human health. With declining fisheries, farmed fish constitute an increasing proportion of the fish in the food basket. n-3 HUFA in farmed fish has been obtained using fish oils (FO), derived from feed grade marine fisheries, in the feeds. This practice is not sustainable, and will constrain growth of aquaculture and will further pressurise these dwindling stocks. In this scenario, sustainable alternatives to FO are urgently required, with vegetable oils (VO) the prime candidates. However, VO are rich in short chain polyunsaturated fatty acids (PUFA) but devoid of the n-3 HUFA abundant in FO. As with all vertebrates, PUFA are essential in the diet of fish, but requirements vary with species. Generally, in marine fish, the dietary requirement is for HUFA, rather than shorter chain PUFA found in VO. Feeding marine fish on VO can reduce health condition, and also lower the n-3 HUFA content of the flesh compromising their nutritional value to the human consumer. HUFA can be biosynthesised from short-chain PUFA in reactions catalysed by fatty acid desaturase enzymes. Evidence suggests that the dependence of marine fish on dietary HUFA is caused by deficiency in the activity of one or more of the key fatty acid desaturase enzyme needed for its synthesis. The objective of this project is to study these enzymes in cobia Rachycentron canadum, a marine fish with a huge growth rate when fed on FO. This growth rate and the production of healthy fish cannot be maintained when fed VO diets and so, as a first step to understanding the mechanisms underpinning the effects of VO feeding, we plan to clone and characterise the fatty acid desaturase enzymes in cobia. Additionally, the project will contribute to diversification of European aquaculture and strengthening of its leadership in global aquaculture sustainability."