Dietary Microencapsulated Roselle (Hibiscus sabdariffa L.) Calyx Extract Enhances Growth, Pigmentation, and Physiological Responses in Fancy Carp (Cyprinus carpio L.).

This study evaluated the optimal dietary inclusion level of microencapsulated roselle (Hibiscus sabdariffa L.) calyx extract (MRE) and its effects on growth, physiological responses, pigmentation, and tissue histology in fancy carp (Cyprinus carpio L.). Fish (27.09 ± 1.14 g) were randomly assigned to 500 L tanks (30 fish/tank) and fed diets containing 0% (MRE-0), 1% (MRE-1), 2% (MRE-2), 3% (MRE-3), and 4% (MRE-4) MRE for 60 days, with three replicates per treatment. Fish fed MRE-2, MRE-3, and MRE-4 showed significantly higher final weight (p = 0.001), weight gain (WG) (p = 0.003), specific growth rate (SGR) (p = 0.003), and average daily gain (ADG) (p = 0.003) than those fed MRE-0 and MRE-1, with MRE-3 and MRE-4 exhibiting the lowest feed conversion ratios (FCR) (p = 0.001). Polynomial regression showed a significant relationship between MRE level and SGR (R 2 = 0.9717), with the predicted optimum at 3.76%, which closely aligning with the observed results. No significant differences were found in survival rate (SR) (90%-100%), hepatosomatic and viscerosomatic indices. Hematological parameters showed significant increases in red blood cell (RBC) counts (p = 0.027), hemoglobin (p = 0.003), total protein (p = 0.033), and immunoglobulin levels (p = 0.001) in MRE-3 and MRE-4 groups. MRE supplementation significantly enhanced lysozyme (p = 0.008) and antioxidant enzyme activities (superoxide dismutase [SOD], p = 0.011; glutathione peroxidase [GPx], p = 0.014), with the highest values in MRE-3 and MRE-4. Redness (a∗) values significantly increased in MRE-3 and MRE-4-fed fish, while lightness (L∗) and yellowness (b∗) remained unchanged. Carotenoid and anthocyanin levels in skin, fin, and muscle increased with higher MRE levels. Histologically, MRE-3 improved intestinal villus height, whereas MRE-4 induced more pronounced hepatic hyaline degeneration. In conclusion, dietary inclusion of 3% MRE was identified as the optimal level for fancy carp, improving growth, feed efficiency, immune and antioxidant responses, pigmentation, and intestinal development without adverse hepatic effects.