Effect of Spent Brewer's Yeast Inclusion as a Feed Additive on Nile Tilapia (Oreochromis niloticus) Production, Colour and Fillet Proximate Composition

While yeasts are often incorporated into aquafeed, research examining the impact of Spent brewer's yeast (SBY) often lacks consideration of associated hop acid constituents. Hop acids are important components of SBY, which differentiate it from other yeast derivatives and often limit their application due to bitter taste. The present study examined the relationship between SBY and its associated hop acid when incorporated into an aquafeed. The effect of SBY on the growth, lysozyme activity, colour and nutritional composition of Nile tilapia (Oreochromis niloticus) over a 10-week nutritional trial was assessed. Four treatment feeds were formulated: a control feed (CTRL) with no SBY or hop acids, a feed with 300 mg hop acids/kg (HA), a 12% SBY-supplemented feed (SBY) and a 12% SBY-supplemented feed with 300 mg hop acids/kg (SBY+HA). One hundred and forty-four fish were distributed into 12 tanks, with each tank randomly assigned one of the treatment diets. Key metrics such as weight gain, specific growth rate, feed conversion ratio, viscerosomatic index, hepatosomatic index, conditioning factor and fillet yield were assessed. Additionally, deboned fillets were evaluated for lightness, a and b(LAB) colour and proximate composition. The SBY-supplemented feed without hop acids (SBY) resulted in lower growth, compared to the control (CTRL). However, the HA feed showed improved growth, compared to the control. Small differences were noted in fillet colour, but no significant differences were found in proximate composition across treatments. This study suggests that SBY, enriched with hop acids, could be a valuable protein supplement in aquafeed, providing production benefits without affecting final fillet quality.