Effects of dietary Astragalus caudiculosus (Boiss & Huet, 1856) supplementation on growth, hematology, antioxidant enzyme activities, and immune responses in rainbow trout (Oncorhynchus mykiss Walbaum, 1792)

The potential dietary utilization of Astragalus caudiculosus (AC) in rainbow trout (Oncorhynchus mykiss) was investigated. Four different fish groups (control, AC1, AC2.5, and AC5) were assigned and received the AC-containing diet for 90 days at the rates of 0, 1, 2.5, and 5%, respectively. Results indicated that the growth performance of the AC supplemented fish improved significantly (P < 0.05). Among non-specific immune parameters examined, while lysozyme activity of the AC supplemented fish increased (P < 0.05), oxidative radical production decreased in AC1 and AC2.5 fish groups (P < 0.05) but did not differ in the AC5 group (P > 0.05) compared to the control. Moreover, myeloperoxidase activity was not affected by the AC supplementation (P > 0.05). All pro-inflammatory and anti-inflammatory cytokine gene expressions, except IL-1β, were up-regulated, especially in the fish groups fed with 2.5 and 5% AC supplemented feed (P < 0.05). AC administration caused an elevation in GPx and G6PDH activities, and a decrease in SOD, CAT, and lipid peroxidation (P < 0.05). Overall, AC extract was found to improve the growth, antioxidant status, and immune response of the fish.