Potential of resveratrol and genistein to influence marine and freshwater fish fatty acid metabolism and performance
The focus of this thesis is the evaluation of a possibility to counteract the dietary induced reduction of lipid quality of farmed fish. The potential of the two bioactive substances resveratrol and genistein to influence the fatty acid metabolism and performance of freshwater and marine fish was assessed as possible tool. The first experiment revealed that the lipid quality of rainbow trout, a fresh water species, was improved when the fish were fed diets with reduced fish oil level and resveratrol supplementation. The combination of these two dietary factors led to a stimulation of enzymes involved in the fatty acid biosynthesis. The second trial revealed that genistein did not influence the lipid quality of trout. Furthermore, both bioactive substances impaired the feed intake and resveratrol led to a reduced performance of the fish. A digestibility trial disclosed that resveratrol and genistein significantly reduce the digestibility of gross energy in trout. An additional histopathological investigation revealed neither damage nor improvement of the intestinal morphology through both substances. A fourth trial was conducted in order to investigate the effects of resveratrol on the Gilthead sea bream, a marine species. Neither a reduction in dietary fish oil level, nor the use of dietary resveratrol affected the growth, performance, and lipid quality of sea bream. A resveratrol-mediated alteration of the lipid quality was solely visible in the livers, when the holding temperature was reduced. The molecular mechanisms behind the fatty acid biosynthesis in sea bream were partly in accordance with results obtained in trout. It was shown, that especially resveratrol has the potential to stimulate the fatty acid biosynthesis, predominantly in freshwater fish. This study contributes to the basic understanding of nutritionally regulated molecular mechanisms and indicates a possible action frame to prevent the dietary induced reduction of fish lipid quality.