Cholesterol is essential in many physiological functions. It gives structure to cell membranes and is a precursor for bile acids, steroid hormones and vitamin D. Vertebrates, like humans and fish, produce their own cholesterol and do not depend on cholesterol from food. Phytosterol, the plant equivalent of cholesterol, is in humans known for its ability to reduce the uptake and production of cholesterol and thus lowering the plasma cholesterol. In Atlantic salmon, high phytosterol concentrations in the diets have been associated with increased levels of fat in liver and plasma.
Insect protein and fat are now becoming realistic ingredients in the diet of farmed Atlantic salmon. Insects cannot synthesize cholesterol and depend on a dietary supply of sterols. Some plant-eating insects do not have access to the animal-derived cholesterol, and have developed the ability to convert plant-derived phytosterol into cholesterol. A conversion of phytosterol into cholesterol could be beneficial for insects as raw material for fish feed and hence for the robustness and health of the salmon.
In the current post-doc project, two different insect species (black soldier fly and kelp fly) will be grown on marine media (tunicates and seaweed). The sterol composition of insects grown on the different media will provide information about their ability to convert phytosterol into cholesterol. The effect of phytosterol on the fish will be investigated by using a cell model and by tracking radio-labelled cholesterol in zebra fish fed different forms of phytosterol. Finally, an Atlantic salmon feeding trial with insect ingredients will be conducted. This work will provide new insights about the use of insects as a source of sterols in the diet of Atlantic salmon.