Growth performance and hematological and antioxidant characteristics of rainbow trout, Oncorhynchus mykiss, fed diets supplemented with Roselle, Hibiscus sabdariffa

Herbal feed additives are important growth-promoters and health-boosters in aquaculture. The present study aimed to assess the effects of dietary Roselle, Hibiscus sabdariffa, supplementation on growth performance, blood stress, and hematological and antioxidant markers in rainbow trout, Oncorhynchus mykiss. Fish were fed 0% Roselle meal (the control), 0.5% Roselle meal (0.5RP), 1% Roselle meal (1RP), and 2% Roselle meal (2RP) diets for 60 days. Growth performance, feed efficiency, survival, stress markers, hematological characteristics, and antioxidant responses were then determined. The highest growth performance (P <= 0.001), survival (P = 0.005), blood erythrocyte (P < 0.001), hematocrit (Hct) (P < 0.001), hemoglobin (Hb) (P < 0.001), plasma and hepatic superoxide dismutase (SOD) (P < 0.001), and catalase (CAT) (P < 0.001) were observed in the 0.5RP treatment (P < 0.05). This treatment also exhibited lower plasma cortisol (P = 0.006), glucose (P = 0.025), hepatic MDA content (P < 0.001), and hemolysis rate (P < 0.001) than that of the control treatment. The 1RP treatment exhibited lower plasma glucose (P = 0.025), hepatic MDA (P < 0.001), and blood hemolysis rate (P < 0.001); as well as higher blood RBC (P < 0.001), Hct (P < 0.001), Hb (P < 0.001), plasma CAT (P < 0.001), and plasma and hepatic SOD (P < 0.001) compared to that of the control. There were no significant differences in any parameters between the control and 2RP treatments, except for the higher blood CAT of the 2RP supplement. The present study demonstrates that RP is a suitable growth- promoter and health-boosting agent in rainbow trout, most likely attributable to its antioxidant properties. Dietary supplementation of 0.5% RP is, therefore, recommended for trout feed supplementation.