Brewer’s yeast as a protein source in the diet of tilapia (Oreochromis niloticus) and freshwater prawns (Macrobrachium rosenbergii) reared in a clear water or biofloc environment Nguyen Huu Yen Nhi Faculty of Veterinary Medicine and Animal Science Department of Animal Nutrition and Management Uppsala Doctoral thesis Swedish University of Agricultural Sciences Uppsala 2019 Acta Universitatis agriculturae Sueciae 2019:21 Cover: Tilapia and giant freshwater prawns next to imhoff cone with biofloc inside (photo: Nguyen Huu Yen Nhi, 2017) ISSN 1652-6880 ISBN (print version) 978-91-7760-360-3 ISBN (electronic version) 978-91-7760-361-0 © 2019 Nguyen Huu Yen Nhi, Uppsala Print: SLU Service/Repro, Uppsala 2019 Brewer’s yeast as a protein source in the diet of tilapia (Oreochromis niloticus) and freshwater prawns (Macrobrachium rosenbergii) reared in a clear water or biofloc environment Abstract This thesis investigated the effects of dietary protein replacement of fishmeal or soybean meal with spent brewer’s yeast (SBY) in farmed tilapia and giant freshwater prawns The effect of rearing tilapia and prawn in two different rearing systems, clear water recirculating aquaculture system (CW-RAS) and biofloc recirculating aquaculture system (Bio-RAS), were also investigated The fish reared in Bio-RAS displayed higher growth, a higher protein efficiency ratio and a lower feed conversion rate than fish reared in CW-RAS This difference between systems was not as apparent in the growth and protein efficiency ratio of freshwater prawns In freshwater prawns, the survival rate was not affected by aquaculture water system nor by the replacement of fishmeal with SBY The growth performance of prawns was not significantly different between any dietary treatments in Bio-RAS or CW-RAS Significant differences were only found between brewer’s yeast replaced fishmeal at 60% in a CW-RAS and at 40% in Bio-RAS Tilapia reared in CW-RAS with replacement of fishmeal with SBY showed a significantly (p