| Summary: | Yeasts are gaining attention as alternative ingredients in fish feeds. The nutritional and health potentials of non-saccharomyces yeasts in fish are scarce in literature. Three non-saccharomyces yeasts; Cyberlindnera jadinii (CJ), Blastobotrys adeninivorans (BA) and Wickerhamomyces anomalus (WA) are the focus of this thesis. The objective of the current thesis was to investigate the nutritional values and health effects of the three selected yeasts in the diets of Atlantic salmon (Salmo salar) with focus on growth performance, intestinal health, gut microbiota, and immune responses of fish. The three yeasts were produced in-house using a growth medium containing a blend of enzymatic hydrolysates of pre-treated spruce wood (Picea abies) and chicken by-products. After harvesting, the selected yeasts were processed by direct heat-inactivation with spray-drying (ICJ, IBA and IWA) or autolyzed at 50 ºC for 16 h, followed by spray-drying (ACJ, ABA and AWA). The present thesis comprises of seven papers. Paper I used a desk study approach to review the state-of-the art on the use of yeasts in fish feeds and identified gaps in literature regarding the use of yeasts as aquafeed ingredients. Yeasts are efficient converter of low-value non-food biomass into high-value resources. Yeasts showed comparatively similar amino acids with fishmeal (FM) and soybean meal (SBM), except for methionine, lysine, arginine, and phenylalanine which need to be supplemented when used in fish feeds. Genetic modification and/or nutrient digestibility through exogenous enzyme supplementation and the use of cost-effective down-stream processing (DSP) are possible strategies to increase the nutritive values of yeasts in fish. Additional investment in large-scale production at competitive price is needed for yeasts to be considered as feasible replacement for FM and SBM in fish feeds. Paper II investigated the impacts of yeast species and processing on performance, immune response and gut health of Atlantic salmon fry fed SBM-based diet in ...
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