New approaches to enhance the endogenous LC-PUFA biosynthesis in rainbow trout
The use of fish oil as a feed ingredient has become a limiting factor in aquaculture production. As a result, vegetable oils are increasingly used as a substitute for fish oil in fish nutrition. This leads to a reduction in the product quality of fish due to lower contents of long-chain polyunsaturated fatty acids (LC-PUFA). The aim of this thesis was to evaluate approaches to enhance the endogenous biosynthesis of LC-PUFA in order to increase the levels of eicosapentaenoic acid (20: 5n-3, EPA) and docosahexaenoic acid (22: 6n-3, DHA) in rainbow trout. Isoflavones are bioactive substances that can influence the fatty acid biosynthesis via various mechanisms of action. Thus, the first experiment investigated different substances to identify those that stimulate the LC-PUFA biosynthesis in rainbow trout. Equol and genistein slightly increased the DHA levels in whole body homogenates compared to the control group. In a second experiment, rainbow trout were fed diets with genistein and equol at different levels. No effect on the fatty acid composition of fish tissues was detected. In the third experiment, the oil of the plant Buglossoides arvensis was examined. The special fatty acid composition of this oil should increase the efficiency of the LC-PUFA biosynthesis. Thus, a diet based on a blend of fish oil and vegetable oils was gradually substituted with this oil. The highest levels of this oil resulted in an increase in EPA fillet levels of rainbow trout compared to those of the control group. In order to increase both EPA and DHA, the fourth experiment evaluated whether the combination of Buglossoides arvensis oil with equol can increase the levels of both fatty acids in the fillet. In comparison to the control group, the LC-PUFA levels were only increased marginally by this combination. In summary, this work shows that the endogenous biosynthesis of LC-PUFA in rainbow trout can be increased by a specific dietary fatty acid composition as well as by bioactive substances and their combination, respectively.