Epsilon Open Archive

Abstract

Healthy long chain polyunsaturated fatty acids are traditionally associated with fish. In farmed fish, the feed previously contained these 'marine' fatty acids. However, the dramatic increase in aquaculture production, accompanied by increased demand for fish-based raw materials for feed production and the static or decreasing supply of fish raw materials, poses a challenge for the aquaculture feed industry. When scarce fish oil is exchanged for vegetable alternates, this is reflected in the fatty acid profile of the fish. Fish fed a vegetable oil-based diet have a lower content of long chain omega 3 (n-3) fatty acids than those fed a fish oil-based diet. This study examined the use of vegetable oils in combination with the bioactive compounds lipoic acid and sesamin in fish feeds. These compunds increased the proportion of long chain n-3 fatty acids in the muscle of pacu (Piaractus mesopotamicus) and rainbow trout (Oncorhynchus mykiss) and in hepatocytes of Atlantic salmon (Salmo salar L). Lipoic acid increased the proportion of eicosapentaenoic acid (EPA, 20:5n-3) in pacu muscle, while sesamin increased the proportion of docosahexaenoic acid (DHA, 22:6n-3) in rainbow trout muscle and Atlantic salmon hepatocytes. A study on lipid uptake and transport in cannulated rainbow trout showed that ingested and de novo synthesised fatty acids cannot be studied separately by blood sampling solely. Sesamin affected expression of lipid-related genes (PPARα and γ, cd36, SRB-I, CPT1, Δ5 and Δ6 desaturase) in Atlantic salmon hepatocytes and PPARα in rainbow trout liver. The desaturation and elongation of radiolabelled 18:3n-3 and radiolabelled β-oxidation products from 18:3n-3 increased in Atlantic salmon hepatocytes incubated with sesamin. The most increased β-oxidation product was acetate, indicating increased peroxisomal β-oxidation. The results presented in this thesis provide information on how lipid metabolism in fish is affected by intake of bioactive compounds. This is useful in finding sustainable alternatives for production of aquaculture feeds and, in turn, of fish muscle with a healthy fatty acid profile.