Nutritional, health, and technical properties of black soldier fly (Hermetia illucens) in Atlantic salmon (Salmo salar) feeds

Black soldier fly (BSF) (Hermetia illucens) has been identified as a promising novel ingredient in fish feeds. The knowledge on optimal downstream processing of BSF is, however, lacking in the literature. The main objective of this thesis was to contribute to increased knowledge on this topic. This thesis presents five papers. Paper I investigated the dose-dependent effects of two differently processed full-fat BSF larvae products in diets for Atlantic salmon (Salmo salar) on technical pellet quality, nutrient utilization, and growth performance. Atlantic salmon pre-smolts were fed full-fat BSF meal or full-fat BSF paste, added to extruded diets, replacing increasing levels of protein from fishmeal and plant protein sources (6.25, 12.5 and 25% by meal and 3.7 and 6.7% by paste). The expansion and water stability of feed pellets numerically decreased with increasing inclusion of BSF meal and paste. Replacement of up to 12.5% and 6.7% of protein with full-fat BSF meal and paste, respectively, did not compromise fish growth performance, but growth rate decreased at 25% meal replacement. Protein digestibility decreased linearly with increasing dietary level of BSF meal or paste, but the protein retention was not affected by dietary BSF inclusion. Subsequently, Paper II investigated the dose-dependent effects of dietary full-fat BSF larvae meal and paste on gut health and systemic immune responses in Atlantic salmon. Replacement of up to 12.5% protein with meal and 6.7% with paste improved gut health by improving distal intestine histology and reducing enterocyte steatosis in pyloric caeca. Replacing 25% protein with full-fat meal did not cause inflammatory changes in distal intestine histology but increased the level of pro-inflammatory cytokine IFNγ in the distal intestine and gave mild to moderate enterocyte steatosis in pyloric caeca. The BSF meal and paste in diets caused minor effects on protein expression in skin mucus and systemic immune responses in fish. Paper III investigated the effect of inclusion of BSF larvae meals and fractions in Atlantic salmon diets on technical pellet quality, nutrient utilization, and growth performance. Atlantic salmon pre-smolts were fed extruded diets containing meals (full-fat, de-fatted or de-chitinized meals) or fractions (oil or exoskeleton) of BSF. Meals replaced 15% protein from fishmeal and plant sources in a control diet. Lipid-rich full-fat and de-chitinized meals in the diets numerically reduced expansion and w