Green synthesized zinc oxide nanoparticles using Scrophularia striata extract attenuate crowding stress responses in common carp.

Nanoparticles have recently been recognized as promising dietary supplements in aquaculture. This study investigated the impact of the green synthesized ZnO nanoparticles (GNP) using Scrophularia striata on growth performance and stress-related markers including innate immune elements, antioxidant capacity, and serum biochemical parameters of the common carp under crowding stress conditions. The common carp (N = 480, 15.48 ± 0.39 g) were fed four experimental diets including GNP0 (control group), GNP10 (10 mg/Kg), GNP 20 (20 mg/Kg), and GNP30 (30 mg/Kg) for 60 days. Following the feeding trial, the fish were subjected to crowding stress for 6 h. Accordingly, the Final weight (FW), weight gain (WG), specific growth rate (SGR), and feed conversion ratio (FCR) exhibited a significant difference in the GNP20 and GNP30 groups when compared to the control. After stress, GNP10-GNP30 diets mitigated the effects of crowding stress on serum and mucus lysozyme (LYZ), serum complement alternative pathway (ACH50), serum immunoglobulin (Ig), and mucus alkaline phosphatase (ALP), serum catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), lipid peroxidation (malondialdehyde; MDA), and serum biochemical parameters except lactate. In addition, the highest antibacterial activity of green-ZnO NPs among bacteria was related to Pseudomonas aeruginosa (22 ± 0.2 mm). The results indicated that dietary green zinc nanoparticles, particularly at a concentration of 20 mg/kg can improve growth performance and attenuate the effects of crowding stress on the physiological responses of the common carp.