## 1 Introduction  
Reactive oxygen species (ROS) are generated as part of the normal metabolic processes and eliminated through enzymatic and non-enzymatic antioxidant defense systems in aerobic organisms [1; 2]. However, the metabolic oxidant/antioxidant equilibrium is broken when the organisms are exposed to abnormal environments, including air pollutants, X-rays radiation, cigarette smoking, and industrial chemicals, which stimulate oxidative stress and generate superfluous and toxic ROS [3; 4]. Those ROS lead to the development of aging and many chronic diseases, such as cardiovascular disease (CVD), inflammation, diabetes mellitus, neurodegenerative disorders, and cancers [5; 6]. In addition, lipid corruption induced by oxidation in food is the main reason for the quality deterioration and shortening the shelf life [7; 8; 9]. At present, artificial antioxidants are generally applied to clear ROS in food and biological systems, but increasing evidence linking artificial antioxidants to negative health influences severely limited their applications [1; 10]. Then, natural compounds, such as peptides, phenols, flavonoids, carotenoids, and vitamins, are continually investigated as the alternative agents of artificial antioxidants due to their significant antioxidant activities and little adverse effects [11]. Antioxidant peptides (APs) isolated from food proteins have drawn great public attention because of their high-level safety and strong ROS scavenging, cytoprotective, and DNA protection capacities [12; 13; 14]. EVSGPGLSPN from walnut could significantly (\(p<0.05\)) reduce ROS generation, and dose-dependently increase cell viability of H\({}_{2}\)O\({}_{2}\)-induced PC12 cells by enhancing the levels of intracellular antioxidant enzymes and blocking the nuclear factor-\(\kappa\)B (NF-\(\kappa\)B)/caspase pathway [15]. IYVVDLR and IYFVVR from alcalase-hydrolysate of soybean could strongly scavenge radicals, upregulate total reduced glutathione (GSH) synthesis, enhance activities of intracellular antioxidant enzyme (catalase (CAT) and glutathione reductase (GR), and suppress ROS-mediated inflammatory responses via inhibiting interleukin-8 secretion in Caco-2 cells [16]. APs from hazelnut by-products [17] and corn gluten [18] exhibited similar cytoprotective effects and intracellular ROS scavenging activities through the upregulation of intracellular antioxidant enzyme and GSH levels. In addition, APs from seafood and their processing by-products such as tuna, cuttlefish, sardinelle, bluefin leatherjacket, tilapia, and shrimp, also have been studied and showed potent antioxidant activities including radical scavenging activity, reducing power, and inhibition ability on lipid and protein oxidation [5; 19]. [PERSON] et al. reported that FPYLRH and GIEWA from protein hydrolysate of miuuy croaker swim bladders could strongly scavenge radicals and effectively inhibit lipid peroxidation [20]. PIIVYWK and FSVVPSPK from _Mytilus edulis_ hydrolysates exhibited strong 2,2-diphenyl-1-picrylhydrazyl radical (DPPH-) scavenging and ORAC activities, and increased cell viabilities in H\({}_{2}\)O\({}_{2}\)-induced hepatotoxicity through upregulating heme oxygenase-1 (HO-1) level under normal and oxidative stress conditions in cultured hepatocytes [21]. WAFAPA and MYPGLA from hydrolysate of blue-spotted stingray surpassed camosine in their abilities to suppress H\({}_{2}\)O\({}_{2}\)-induced lipid oxidation and protected plasmid DNA and proteins from Fenton's reagent-induced oxidative damage [22]. Therefore, marine proteins are high-quality raw materials for the preparation of APs with the ability to enhance health by reducing oxidative stress. Monkfish (_Lophius litulon_) belongs to the family of Lophiidae and is a common commercial fish with the production of approximately \(2\times 10^{5}\) tons/year [7].