Growth performance, biochemical parameters, and digestive enzymes in common carp (Cyprinus carpio) fed experimental diets supplemented with vitamin C, thyme essential oil, and quercetin

Herbal additives and vitamins have gained considerable attention to improve fish health. This study investigates the effects of vitamin C (VC), Thymus vulgaris L. essential oil (TE), and quercetin (QR) supplementation on growth performance, digestive enzyme, body composition, and biochemical parameters of common carp (Cyprinus carpio). Four hundred and twenty fish weighing 20.46 +/- 0.07 g were randomly divided into seven experimental treatments in triplicates. Experimental diets were containing as T1 (0, control), T2 (500 mg/kg VC), T3 (1000 mg/kg VC), T4 (1% TE), T5 (2% TE), T6 (200 mg/kg QR), and T7 (800 mg/kg QR). Fish were fed 3% of body weight daily for 60 days. According to the results, the groups fed with experimental diets showed the higher final weight, weight gain (WG), specific growth rate (SGR), and survival rate (SR) and lower feed conversion ratio (FCR) compared to the control group (p < .05). Regarding biochemical indices results, T5, T6, and T7 significantly had the higher serum total protein (TP) than the control (p < .05). Meanwhile, albumin (ALB) showed no significant difference in all groups (p > .05). All the supplemented groups were found to have significantly lower creatinine (CRT), glucose (GLU), and urea (UR) and higher globulin (GLO) content compare to the control (p < .05). Moreover, T3, T4, and T5 showed a significant decrease in triglyceride (TRIG) levels compared to the control (p < .05). Cholesterol (CHOL) activity in T4 supplemented group was significantly lower than the control (p < .05). Also, cortisol (CORT) recorded a significant decrease in T6 and T7 compared to the control (p < .05). Lactate dehydrogenase (LDH) had a significantly lower level in T4, T6, and T7 compared to the control (p < .05). The whole fish body composition was not affected by the feed additives and the control (p > .05). Besides, significant enhancements were observed in cases of intestine protease, amylase, and lipase enzymes in all the supplemented groups compared to the control (p < .05). In conclusion, the present results demonstrated that VC, TE, and QR could effectively improve survival, growth performance, and biochemical indices in C. carpio.