Effect of climate change on hematotoxicity/hepatoxicity oxidative stress, Oncorhynchus mykiss, under controlled conditions

temperature treatments. SOD activity/concentration increases in the suppression of potential damage caused by this temperature change. In our research findings, the expected concor- dance between SOD, CAT and GPx enzyme activities was determined. Therefore, the accumu- lation of SOD and CAT enzymes was used to reduce the accumulation of oxidative damage by ROS, which is highly harmful. The optimum growth temperature for rainbow trout is given as 11˚C in the literature [57]. Same researcher reported that temperature and flow rate changes negatively affected reproduction and growth in rainbow trout. Similar to our results, it was found that CAT enzyme was up-regulated in temperature increases and this increase increased lipid oxidation. These results suggest that increases in SOD and CAT are effective in LPO damage in rainbow trout and differences in temperature changes strengthen the possibility of oxidative stress in fish [54]. SOD activity may have increased in both tissues to prevent oxidative stress caused by increased mitochondrial density. Increased SOD activity in both muscle and liver suggests that posttranslational modifications regulate SOD activity [58]. SOD scavenges oxygen free radicals in the body, CAT decomposes hydrogen peroxide into water, GPx reduces lipid peroxides to alcohols and tries to minimize the possibility of lipid oxidation and the damage caused by MDA to cells [9]. In our research findings, it was determined that these three enzymes cooper- ate to complete the antioxidant process.

The findings are supported by enzyme changes and increase in MPO and MDA that tem- perature causes a stress in rainbow trout. Oxidants/antioxidants can interact with each other, leading to overlapping effects [59]. From the available data, it appears that the oxidative state in the tissues and the relationship between TOS and TAS depend on temperature [60]. Regard- ing oxidative stress, TOS in the tissues increased at other temperatures compared to the opti- mal survival temperature and correlated with the MDA/MPO level of both tissues. Therefore, up-regulation of SOD in most tissues and general depression of this antioxidant enzyme sug- gest an increase in the level of hydrogen peroxide after thermal stress. Therefore, depression of antioxidant enzymes may be a defense strategy to help with the effectiveness of the immune system [61]. Oxidative stress participates in different cellular functions by acting as a second messenger in signal transduction. Nevertheless, they can also cause cellular damage, including oxidative damage to proteins and DNA, which creates lipid peroxidation. The thermal stress can lead to a state of oxidative stress in aquatic organisms. It has been previously observed that thermal stress can modulate the oxidative stress state in teleost fish’s various tissues [49]. The thermal stress at low temperatures has been reported in dairy fish (Chanos chanos) as increasing anti- oxidant enzymes and oxidative damage [62], while lipid peroxidation has been observed in

Piaractus mesopotamicus under the same stressor effect [61, 63, 64]. Furthermore, lipid peroxi- dation may vary by species. It has been stated that carnivorous species have very low GPx activ- ity and the highest SOD/ CAT activity in the liver, compared with herbivorous and omnivorous species, and that these differences may be effective in enzymatic antioxidant sys- tem activities [60]. This is consistent with the findings of our study, which showed that thermal stress exerts a significant oxidative effect on rainbow trout muscle and liver. In addition, the identification of significant increases in enzyme activity with tempera- ture changes is consistent with different studies conducted [65]. It suggests that an increase in antioxidant enzymes may protect against the harmful effects of oxidative damage caused by heat stress. Our research found that the MDA content in D in all tissues was significantly higher than in A; this indicates that oxidative stress occurs during high temperature, and the cells are damaged. The thermal stress associated with oxidative stress can vary by spe- cies and tissues, and the liver is considered a sensitive organ in determining this thermal stress [49]. PLOS ONE Effect of temperature on fish physiology and biochemistry PLOS ONE | https://doi.org/10.1371/journal.pone.0294656 November 30, 2023 9 / 13