Use of residues from plant oil production to manufacture high-quality fish feed

Fish production via aquaculture is a growing industry and there is a need to make this sustainable. In this regard, the fish feed that is currently used plays a not insignificant role. The main components of conventional fish feed are fish oil and fish meal and these are becoming ever scarcer due to overfishing. If these two components can be replaced by renewable raw materials, for example residues from plant oil production, then this would significantly increase the sustainability of the aquaculture industry. Oil press cake, a residue from oil seed processing, contains considerable concentrations of valuable substances such as proteins, lipids, and natural antioxidants. It is hence an ideal starting material for manufacturing a sustainable fish feed.

The now ended research project Örüfimi carried out by the Fraunhofer IVV successfully developed and tested the first fish feed manufactured on this basis. The objective of the ongoing follow-up project is to further improve the quality of the fish feed. The particular focus of the research work is to enhance the acceptance and digestibility of the fish feed, and so achieve high fish growth rates.

Besides containing valuable substances, the protein-rich press cake obtained from plant oil production also contains antinutritive components such as bitter tasting secondary plant ingredients and these lower the acceptance of the fish feed to fish. This can be remedied by lowering the concentrations of these substances and simultaneously adding appetence-promoting raw materials such as mussel meal or krill meal.

Changes to the feed formulation not only affect the nutritive properties but also the technofunctional properties of the fish feed. The morphology, sink speed, and mechanical stability of the fish feed are particularly important factors for effective commercial use.

One of the main challenge of the project work is to adapt the parameters used for the extrusion process (e.g. temperature, screw speed, and water addition) in order to produce stable fish feed pellets.