The cost of feeding takes the highest part of aquaculture production cost; protein sources are the most expensive feed ingredient. Insects have been proposed as an alternative protein source and they are especially well suited for carnivore species because European perch already consume more than 50% insects in their natural diet. To develop an effective feed formulation an understanding of the digestive processes is important. The research conducted during this dissertation explored the nutrient composition of yellow mealworm (YM), optimization of production, and nutrient composition of YM and compared the growth, protein efficiency ratio (PER), net protein ratio (NPR), and true digestibility (TD) of diets containing 25% and 50% yellow mealworm meal to soybean meal using a rat assay. We continued to gain a proper understanding of the digestion processes of the European perch, by investigating the enzyme activity at different temperatures lower than the reported optimal. The various experiment provided a basis for the formulation of a diet where various percentages of fishmeal were replaced with yellow mealworm meal, this diet was used in a feeding experiment. We explored the nutrient composition of YM at different ages, sizes, and stages of life cycle. The result shows that larvae do not differ based on age, but the size influences the nutrient composition, the larger-sized worm had lower surface area hence a lower proportion of exoskeleton and higher dry matter content. We also used duckweed as a feeding substrate to determine its effect on production parameters and nutrient composition of YM, the result indicates that above 50% inclusion of duckweed in the feeding substrate result in worse production parameters. When we considered the result of the production parameters and the nutrient composition in this experiment the S75D25 feeding substrate is the best. In an in-vivo rat experiment where soybean meal was replaced with 25% and 50% YM meal the biological values were not statistically different from those fed 100% soybean meal as a protein source. This means that up to 50% replacement of soy with YM meal maintained the quality of protein as seen in the PER, NPR, and TD.

The result of enzyme activity at different temperatures shows that the highest enzyme activity is between 18 °C and 20 °C, the enzyme activity peaks at 20 °C after which there is a decline in the enzyme activity. When European perch were fed with feed formulated by replacing 12.5%, 25%, and 37.5% fishmeal with YM meal. The result shows that at all 3-inclusion levels, there is no significant difference in production parameters, hence YM meal can replace fishmeal up to 35.7% without adverse effects on the growth rate, FCR, and survival rate.