Effects of Dietary Rhodotorula mucilaginosa Powder Supplementation on Growth, Coloration, and Health in Fancy Carp (Cyprinus carpio Linn.).

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.