## 1 Introduction  
Rainbow trout (_Oncorhynchus mykiss_) is one of the most important freshwater fish species for an increase in the world trade of fish and fish products [1]. Nevertheless, trout is highly susceptible to oxidative degradation due to high unsaturated and saturated fatty acids ratio (5.23), high amount of protein (20%) and low stability related to conformation and structure of the hemoglobin [2; 3; 4].  
The oxidative degradation is the main non-microbiological reason to off-flavor, discoloration, loss of texture, and formation of toxic compounds in the postmortem period, which are determinant factorsto shorter shelf life, rapid loss of overall quality and consumer rejection [5; 6]. Currently, the loss of quality from capture to final consumption results in a discard of 27% of the fish, and it is the main limiting factor to increase worldwide commercialization and consumption of fish [1]. To overcome this challenge, the United Nations Food and Agriculture Organization [1] suggests studies concerning viable preservation technologies aiming to achieve a maximum shelf life without compromise the original quality parameters of fish, which is one of the most challenges for the scientific community and food industry by the use of a single method. In this way, studies about combined preservation treatments have increased [7; 8; 9; 10].  
UV-C radiation is a promising non-thermal technology for the fish production chain. Beyond the proven efficacy to decrease the bacterial growth rate during refrigerated storage of fish species, UV-C has low cost, does not generate toxic residues and can be easily implemented in the fishery industry without changing the production flow [9; 11; 12]. The effects of UV-C depend mainly on the dose used, food composition, type and load of microorganisms into the food matrix [11; 12; 13; 14]. Nevertheless, in general, UV-C doses (0.10-0.30 J/cm\({}^{2}\)) needed to reach a shelf life extension of 2-6 days in refrigerated fish species, including rainbow trout, lead to one or more oxidative damages by producing reactive oxygen species (ROS) compromising overall fish quality, which is the main limiting factor for the use of UV-C at industrial scale [9; 12; 13; 15; 16].  
O\({}_{2}\) scavenger or O\({}_{2}\) absorber has been used preferentially to vacuum packaging (VP) and modified-atmosphere packaging (MAP) due to its ability to reduce and maintain the O\({}_{2}\) concentration inside the package at levels less than 0.01% being effective against oxidative degradation from ROS and growth of obligate aerobic microorganisms during the entire storage period [10; 17; 18]. O\({}_{2}\) scavengers contain compounds in powder such as ascorbic acid, catechols, sulfites, and mainly iron and ferrous oxide [18], which result in a constant oxygen consumption by oxidation of ferrous oxide (FeO) in ferric oxide (Fe\({}_{2}\)O\({}_{3}\)) [17; 18]. Furthermore, O\({}_{2}\) scavengers are mainly sold in sachet form at low cost and do not require the use of equipment. At the present moment, it is known that O\({}_{2}\) scavenger extends the shelf life in 5-7 days while prevents the oxidation during refrigerated storage of fish species, including rainbow trout [7; 9; 19]. Therefore, O\({}_{2}\) scavenger could be a simple and effective alternative to mitigate the adverse effects of UV-C radiation.  
Despite these facts, there is only one recent study evaluating the combined effect of O\({}_{2}\) scavenger and UV-C radiation in tilapia fillets stored under refrigeration [9], however rainbow trout is more prone to oxidative degradation than tilapia [2; 3; 13]. In this context, this study aimed to investigate the effect of oxygen-scavenger packaging and two UV-C doses (0.102 and 0.301 J/cm\({}^{2}\)), alone or in combination, on oxidative stability, instrumental color and texture parameters of rainbow trout (_Oncorhynchus mykiss_) fillets stored at 4 \(\pm\) 1 \({}^{\circ}\)C for 9 days.