The growth performance, feed efficiency, intestinal histo-morphological indices, antioxidat ive status, and related genes of Nile tilapia (Oreochromis niloticus) fed fermented rice hulls

Fermentation of plant-originated by-products, including rice hulls (RH), is suggested for the sustainability of the aquafeed industry. Hence, using processed agriculture by-products can be a feasible and effective solution to produce high feed quality at low cost. In this study, fermented rice hulls (FRH) were included in Nile tilapia diets at 50, 100, 150, and 200 g/kg. Further, fish offered FRH-free diet (Ctrl) and non-fermented rice hulls (NFRH). 270 Nile tilapia juveniles with an average initial weight of 19.54 ± 0.32 g/fish were distributed in six groups (triplicates), and the six respective test diets (NFRH, Ctrl, FRH5, FRH10, FRH15, and FRH20) were offered for 75 days. The results showed that final body weight (FBW), weight gain, specific growth rate (SGR), and protein efficiency ratio were increased while the feed conversion ratio was markedly reduced (P < 0.05) by dietary FRH compared to fish-fed NFRH. The regression analysis showed that the maximum FBW and SGR can be reached by dietary inclusion of FRH at 137.5 to 157 g/kg (P < 0.05). The fish-fed with dietary FRH15 showed higher carcass crude protein content than fish-fed NFRH (P < 0.05). Dietary NFRH triggered catarrhal inflammation of the intestinal villi and separation of the degenerated apical part of the intestinal epithelium. Interestingly, the elevated concentration of FRH caused prominent improvement at the level of villous height and goblet cells in the anterior part and increased branching of intestinal villi in the middle and posterior segments, particularly at the higher levels (FRH15 and FRH20) (P < 0.05). Further, activities of digestive enzymes (amylase, lipase, and protease) showed improved values in fish-fed FRH in a dose-dependent manner (P < 0.05). The relative expression of GHR1, IGF-1, FABP, and CD36 genes was markedly higher in fish-fed FRH15 and FRH20 than in the Ctrl and NFRH diets (P < 0.05). Moreover, antioxidative-related genes (CAT, SOD, and GPX) showed upregulated mRNA expression levels by dietary FRH20 (P < 0.05). In summary, it can be suggested that dietary FRH can be included up to 200 g/kg in Nile tilapia feed without compromising the growth performance, feed digestion, intestinal health, and antioxidative status.