Oxidative stress and use of antioxidants in fish semen cryopreservation Leydy Sandoval-Vargas 1,2 , Mauricio Silva Jim ´ enez 3 , Jennie Risopatr ´ on Gonz ´ alez 4 , Elı ´as Figueroa Villalobos 5 , Elsa Cabrita 6 and Iv ´ an Valdebenito Isler 5 1 Faculty of Natural Resources, Catholic University of Temuco, Temuco, Chile 2 Faculty of Agricultural Science and Natural Resources, Research Group on Aquatic Organism Reproduction and Toxicology – GRITOX, Aquaculture Institute, University of los Llanos, Villavicencio, Colombia 3 Nucleus of Research in Food Production, Department of Veterinary Sciences and Public Health, Catholic University of Temuco, Temuco, Chile 4 Faculty of Medicine, Center of Biotechnology on Reproduction (BIOREN-CEBIOR), University of La Frontera, Temuco, Chile 5 Nucleus of Research in Food Production, Faculty of Natural Resources, Catholic University of Temuco, Temuco, Chile 6 CCMAR-Centre of Marine Sciences, University of Algarve, Faro, Portugal Correspondence Iv ´ an Valdebenito Isler, Nucleus of Research in Food Production, Faculty of Natural Resources, Catholic University of Temuco, Rudecindo Ortega 02950, Temuco, Chile. Email: ivisler@uct.cl Received 1 April 2020; accepted 25 June 2020. Abstract Reactive oxygen species (ROS) have been proposed as one of the main causes of the impairment of fish spermatozoa integrity and functionality during cryopreser- vation. The high content of unsaturated fatty acids in sperm cells and the low antioxidant capacity of diluted semen are key factors in making sperm cells sus- ceptible to ROS attacks. For this reason, some recent studies have determined the antioxidant status of the seminal plasma and spermatozoa of fish species. Addi- tionally, some studies have evaluated the effects of antioxidants on post-thaw sperm quality. Although ROS are certainly involved in sperm damage, other fac- tors, such as ice crystal formation, seem to play a crucial role in cryodamage. This challenge has not yet been resolved because both the endogenous antioxidant capacity of the semen and its response to different supplementation practices seem to present specific inter- and intraspecies characteristics and effects. This review summarises knowledge on antioxidant defence and oxidative stress in fish semen, as well as antioxidant supplementation in cryopreservation media, in order to establish perspectives for future studies. Key words: antioxidative defence, fish spermatozoa, free radicals, oxidative damage, ROS pro- duction, sperm function. Introduction Fish sperm cryopreservation offers a large number of bene- fits extensively described in previous reviews (Suquet et al. 2000; Cabrita et al. 2010; Martı ´nez-P´ aramo et al. 2017). From the first work of Blaxter in 1953 down to the begin- ning of this century, more than 200 studies of fish semen cryopreservation have been published. Significant progress has been made in developing this technology through the modification of several factors such as type and concentra- tion of cryoprotectants, dilution rate, freezing/thawing rates and packaging systems (Cabrita et al. 2001; Dziewulska et al. 2011; Ciereszko et al. 2014; Viveiros et al. 2015). How- ever, post-thaw sperm quality is still low in some species compared with fresh semen in terms of motility and fertil- ity rates (Galo et al. 2011; Asturiano et al. 2016; Purdy et al. 2016). The toxicity of cryoprotectants combined with osmotic shock and the formation of ice crystals during freezing and thawing have been described as one of the main factors of cryodamage (Mazur 1963; Parks & Graham 1992; Meyers 2005). In addition, several authors have shown that cryopreservation increases reactive oxygen spe- cies (ROS) production (Li et al. 2010c; Klaiwattana et al. 2016; Mostek et al. 2018; Figueroa et al., 2019). Reactive oxygen species is the term generally used to describe oxygen-derived pro-oxidants (Kohen & Nyska 2002). They play a dual role in biological systems, either beneficial or harmful depending on their nature, concentra- tion, location and time of exposure (Guerriero et al. 2014; Aitken 2017). ROS can be divided into 2 groups: (i) radicals and (ii) non-radicals. Radical species include the superox- ide anion (O ÁÀ 2 ), hydroxyl radical (OH • ), peroxyl radical © 2020 John Wiley & Sons Australia, Ltd 1 Reviews in Aquaculture, 1–23 doi: 10.1111/raq.12479