| Summary: | Aquaculture intensification and sustainability concerns have prompted research into new feed ingredients, notably microbial ingredients such as yeast. Cyberlindnera jadinii (CJ) and Wickerhamomyces anomalus (WA) are among the functional protein sources with immunostimulatory effects that are currently explored as novel ingredients for fish feeds. In this study, the two yeast species were grown on sugars from hydrolyzed wood and nitrogen from hydrolyzed chicken offal and subjected to two forms of downstream processing of either autolysis (16 hrs, 500 C) or direct inactivation by spray drying. The objective of this research was to determine how two yeast species with different downstream processing counteract soyabean meal induced enteritis (SBMIE) in Atlantic salmon (Salmon salar L.) during seawater transfer using morphometry, histomorphology and immunohistochemical techniques. The experiment was conducted on post-smolt of Atlantic salmon fed in triplicates a fishmeal (FM) control diet (negative control), a diet containing 30% SBM (positive control) and four treatment diets containing 30% SBM supplemented with 10% yeast either inactivated or autolyzed. The results indicate that 10% inclusion of both C. jadinii and W. anomalus (when inactivated or autolyzed) had no negative effect on growth and feed conversion. Histological observations on the submucosa and lamina propria cellularity also indicate that inactivated C. Jadinii has the potential to prevent SBMIE in Atlantic salmon. No differences in the CD3e + population was observed across diets but similarity between lamina propria CD8a+ labelled cells between the FM and the yeast containing diets was observed. This indicates that the yeast had some immunostimulatory effect. Crude lipids were better digested in C. Jadinii while inactivation resulted in the release of more b-glucans. To conclude, the potential of yeast to alleviate SBMIE depends on the yeast strain and the downstream processing. Foods of Norway submittedVersion M-FT
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