Einsatz von Mikroalgen mit optimiertem Stearidonsäuregehalt für die Fischernährung

New feed ingredients are currently of high interest due to the rising aquaculture production. Various plant materials are already in use as fish oil substitutes, however, the provision of essential n-3 fatty acids needs to be ensured. Freshwater fish are capable of biosynthesizing n-3 long-chain fatty acids if sufficient precursor fatty acids are available. Microalgae have great potential as lipid sources due to their diverse fatty acid profiles. In this thesis, different microalgae species rich in stearidonic acid were tested in diets for rainbow trout. In a first trial, differently processed meals of Tetraselmis chui and Isochrysis galbana were used, and their apparent digestibility coefficients were determined. The microalgae species, rather than the processing method, affected the digestibility. Both microalgae were then used in a subsequent feeding trial to substitute fish oil and to evaluate their applicability in fish diets in terms of growth performance. After 8 weeks of feeding until apparent satiation, the fish fed microalgae diets displayed a higher feed intake. The fatty acids of the microalgae were successfully metabolized by the fish, and higher dietary DHA levels did not seem to influence the fatty acid biosynthesis. In an additional feeding trial, T. chui was included in diets at different ratios. After 12 weeks of restrictive feeding, the growth rate of the fish was reduced with increasing dietary algae inclusion. However, the DHA-biosynthesis was enhanced and the fillets of fish fed the microalgae diets demonstrated comparable DHA contents. The selected microalgae for this thesis showed promising results and great potential as a fatty acid source in diets for rainbow trout. Furthermore, important insights into the fatty acid biosynthesis were gained. Especially in combination with vegetable oils, these microalgae could serve as driving factors towards sustainable aquaculture feed production.