Nut grass (Cyperus rotundus Linn.) is a weed that grows in all tropical, subtropical and temperate regions of the world, including areas where it grows on saline soil. This research was conducted to evaluate the effect of C. rotundus tuber extract in the diet on the growth performance and disease resistance of Nile tilapia. Various components of phytochemical importance of nut grass, including sugars/carbohydrates, terpenoids, tannins, and flavonoids were found in C. rotundus. Tilapia (n = 25 fish/group in triplicate) were fed with different levels of nut grass extract including 0 (control; T1), 0.4 (T2), 0.8 (T3), and 1.6 (T4) g/kg for 60 days in a completely randomized design (CRD) experiment. After the feeding trial, the highest weight gain and average daily gain (ADG) were observed in the T4 group, but it was not significantly different from T3 (Nile tilapia fed with a 0.8 g/kg) (p > 0.05). The lowest feed conversion ratio (FCR) was observed in the T3 group. Moreover, the fillet, crud lipid content, and blood chemical profiles (aspartate aminotransferase (AST), cholesterol, and malondialdehyde (MDA)) in fish fed with 1.6 g/kg were highest when compared in all groups. In addition, the T3 group presented with the immune response parameter found in red blood cells (RBC), lysozyme activity, and antioxidant (superoxide dismutase activity (SOD)) being higher than those of the control group (p < 0.05). The highest survival (93.33%) was observed in fish fed with 0.8 g/kg (T3) after a 14 day challenge with Streptococcus agalactiae. Thus, it was concluded that nut grass extract at 0.8 g/kg can be used to improve the growth performance and the tendency for resistance to S. agalactiae in Nile tilapia.

Dietary carotenoids and functional feed additives are increasingly used in ornamental aquaculture to improve fish coloration, growth performance, and health. This study evaluated the effects of dietary Rhodotorula mucilaginosa powder on growth performance, feed utilization, pigmentation, physiological responses, hepatic gene expression, and tissue morphology in fancy carp (Cyprinus carpio Linn.). Fish were fed five isonitrogenous and isoenergetic diets containing 0, 0.5, 1, 2, or 4 g/kg R. mucilaginosa powder for 70 days. Fish fed 0.5 g/kg achieved the highest weight gain (25.38 ± 1.56 g) and average daily gain (0.36 ± 0.02 g/day), while 0.5 and 1 g/kg significantly improved feed conversion ratio (1.63 ± 0.03 and 1.70 ± 0.04, respectively) compared with the control and higher inclusion levels (p < 0.05). Supplementation with 2 g/kg produced the greatest skin redness (CIE a* = 17.94 ± 0.34) and skin carotenoid content (15.62 ± 0.89 µg/g) (p < 0.05). Lower inclusion levels also significantly improved intestinal morphology and upregulated hepatic CAT, SOD, IL-1β, VTG, and HSP70 expression (p < 0.05), whereas serum biochemical parameters, cortisol concentration, survival, and liver histopathology remained unaffected (p > 0.05). Overall, R. mucilaginosa powder is a safe multifunctional feed additive. Dietary inclusion of 0.5–1 g/kg is recommended to optimize growth and feed efficiency, whereas 2 g/kg is optimal for enhancing pigmentation. These findings support the development of sustainable natural pigment-based functional feeds for ornamental aquaculture.