Effect of hop acid inclusion as a feed additive on Nile tilapia, Oreochromis niloticus, production, lysozyme activity, fillet color, and aroma

Hop acids are known for their potent antimicrobial properties and may offer significant benefits in aquaculture. As hop acids are a prominent component of spent brewer's yeast, a major byproduct of the brewing industry, their utilization in fish feed holds potential for enhancing both the economic and environmental sustainability of aquaculture operations, provided they are not detrimental to the growth and quality of the product. A 56-day nutritional trial was conducted that incorporated hop acids (Humulone and Lupulone) into the diets of Nile tilapia, Oreochromis niloticus, and assessed their effects on rearing production, lysozyme activity, and final fillet LAB color & aroma. Four experimental diets containing between 0 and 1200 mg hop acids/kg feed were formulated for the nutritional study. Ninety-six tilapias were distributed equally among twelve ~2000 L tanks (eight fish/tank) and randomly assigned a treatment diet with 3 tanks per treatment (n = 3). Fish were weighed weekly and fed daily. After the trial, various production metrics, including weight gain, feed conversion ratio, viscerosomatic index, hepatosomatic index, condition factor, and fillet yield, were assessed. Additionally, lysozyme activity was assessed in isolated serum samples. Skinned and deboned fillets were assessed for LAB color, and a sensory panel evaluated the aroma of raw and baked fillets. The study revealed the inclusion of hop acids provided no significant differences in the production metrics, except for the viscerosomatic index. While not reflected in the FCR, weekly weight measurement found that the feed treatment of approximately 300 hop acids/kg of feed had slightly higher average fish weight per tank toward the end of the feed trial. There were minor differences in color, but no significant differences in aroma between treatment and control fillets. Incorporating hop acids into the diet, even at the highest inclusion level tested, did not result in any adverse effects on the fish. While these findings do not show significant benefits of hop acid addition, there were no detrimental effects, suggesting a promising avenue for utilizing brewing waste streams or isolated hop acids as an effective supplement in fish feed formulations.