The role of spent coffee ground extracts as natural antioxidant supplements in the diet of Nile Tilapia (Oreochromis niloticus)

This study evaluated the potential of spent coffee grounds extract (CGE) as an antioxidant supplement in the diet of Nile tilapia (Oreochromis niloticus). Four experimental diets with varying CGE levels were formulated: 0% (CGE0, control), 2% (CGE2), 4% (CGE4), and 6% (CGE6). Nile tilapia (initial mean body weight = 38.65 ± 0.85 g) were cultured in fiberglass tanks at a stocking density of 20 fish/m2 under continuous aeration. The fish were fed three times daily at 5% of their total body weight. After an 8-week experimental period, the fish fed CGE-supplemented diets exhibited significantly higher growth rate compared to the control group, with CGE4 showing the most pronounced improvement in final body weight (P = 0.027) and weight gain (P = 0.050). However, no significant differences were observed in average daily growth (P = 0.054), specific growth rate (P = 0.256), survival rate (P = 0.487), and feed conversion ratio (P = 0.105) between the dietary treatments. Fish on the CGE6 diet exhibited the highest total plasma protein (P = 0.001) and immunoglobulin levels (P = 0.000). Moreover, CGE supplementation enhanced superoxide dismutase (P = 0.000) and glutathione peroxidase (P = 0.016) activities relative to the control group. The histopathological analysis showed significantly longer intestinal villi in fish fed CGE-supplemented diets, with the longest villi observed in the CGE6 group (P = 0.000). Fish fillets from the CGE6 group exhibited the highest springiness, while hardness was comparable between CGE6 and CGE4 but significantly higher than in CGE2 and CGE0. Additionally, CGE supplementation significantly influenced the colour expression, increasing lightness (L*) while decreasing redness (a*) and yellowness (b*) values. These findings indicate that 4% CGE supplementation is the most effective concentration, as it significantly promotes growth as evidenced by the highest weight gain, while also enhancing blood biochemical parameters, flesh quality, and antioxidative responses in Nile tilapia.