Dietary Olive Leaf Extract Differentially Modulates Antioxidant Defense of Normal and <i>Aeromonas hydrophila</i>-Infected Common Carp (<i>Cyprinus carpio</i>) via Keap1/Nrf2 Pathway Signaling: A Phytochemical and Biological Link

Abstract

Olive leaves are an immense source of antioxidant and antimicrobial bioactive constituents. This study investigated the effects of dietary incorporation of olive leaf extract (OLE) on the growth performance, hematobiochemical parameters, immune response, antioxidant defense, histopathological changes, and some growth- and immune-related genes in the common carp (Cyprinus carpio). A total of 180 fish were allocated into four groups with triplicate each. The control group received the basal diet without OLE, while the other three groups were fed a basal diet with the OLE at 0.1, 0.2, and 0.3%, respectively. The feeding study lasted for 8 weeks, then fish were challenged with Aeromonas hydrophila. The results revealed that the group supplied with the 0.1% OLE significantly exhibited a higher final body weight (FBW), weight gain (WG%), and specific growth rate (SGR) with a decreased feed conversion ratio (FCR) compared to the other groups (p A. hydrophila challenge (p C. carpio’s digestive capacity pre- and post-challenge, presenting the highest activity of protease and alkaline phosphatase (p p A. hydrophila (p sod, nrf2, and protein kinase C transcription levels was detected as a vital approach for the prevention of both oxidative stress and inflammation compared to the infected unsupplied control group (p w/w can be included in the C. carpio diet to improve the growth, antioxidant capacity, and immune response under normal health conditions along with regulating the infection-associated pro-inflammatory gene expressions, thus enhancing resistance against A. hydrophila.

Keywords

• olive leaf extract
• <i>C. carpio</i>
• <i>Aeromonas hydrophila</i>
• antioxidant
• immunostimulant
• gene expression