## 3 Results
### Animal Condition and Tissue Neuroxidative Responses
eliciting a significant inhibition of CAT activity in relation to all treatments, including its contaminated counterpart treatment (i.e., CONT + A; \(p\) = 0.0002 Student's \(t\)-test; Figure 2b). In opposition, fish brain revealed significantly higher CAT activity in the CONT + A treatment (\(93.7\pm 7.8\) mmol-min\({}^{-1}\)-mg\({}^{-1}\) protein; \(p<0.05\)) compared to all treatments (Figure 2c). Moreover, in this tissue, both Hg and abiotic stressors significantly increased CAT activity, although different trends were observed according to stressor interactions. For instance, Hg exposure significantly enhanced CAT in treatments exposed to 19 \({}^{\circ}\)C (i.e., under control (CTR) and A conditions; \(p<0.05\) Student's \(t\)-test), whereas Hg exposure significantly diminished CAT activity in treatments exposed to 24 \({}^{\circ}\)C and 8.0 pH units (i.e., in CONT + W vs. non-CONT + W; \(p\) = 0.003 Student's \(t\)-test; Figure 2c). Figure 2: _Cont._  
SOD activity (percentage inhibition) in _S. senegalensis_ tissues is presented in Figure 3. Overall, the liver presented higher percentages of SOD inhibition (between 89.0% and 91.1%) compared to muscle (between 62.4% and 90.0%) and brain (between 70.5% and 78.5%), regardless of treatment. As for the effect of the three studied stressors, different trends were observed in each fish tissue. Starting with muscle, increased temperatures impaired SOD activity in non-contaminated fish (i.e., 90.0% \(\pm\) 2.5% of inhibition in non-CONT + W treatment; \(p\) \(<\) 0.05), but this trend was counteracted by Hg exposure, especially when acidification also interacted (i.e., 62.4% \(\pm\) 4.9% of inhibition in CONT + A + W treatment; \(p\) \(<\) 0.05; Figure 3a). In the liver, Hg exposure was also associated with lower SOD inhibition, although significant differences between non-contaminated and Hg-contaminated counterparts were only observed in fish exposed to 19 \({}^{\circ}\)C and both pH levels (CTR conditions: \(p\) = 0.003 Student's \(t\)-test; A conditions: \(p\) \(<\) 0.000 Student's \(t\)-test; Figure 3b). Noteworthy, in the liver of non-contaminated fish, significantly higher SOD inhibition was found under acidification alone (97.8% \(\pm\) 0.5% of inhibition in non-CONT + A treatment; \(p\) \(<\) 0.05) compared to all treatments, whereas significantly lower inhibition was observed when acidification was combined with warming (89.0% \(\pm\) 1.2% of inhibition in non-CONT + A + W treatment; \(p\) \(<\) 0.01; Figure 3b). In fish brain, overall, SOD activity did not present significant differences among treatments (percentage inhibition around 70% in most cases; \(p\) \(>\) 0.05), with the exception of fish co-exposed to acidification and Hg which revealed significantly higher inhibition than its non-contaminated counterpart (78.5% \(\pm\) 3.0% of inhibition in Hg + A treatment; \(p\) = 0.01 Student's \(t\)-test; Figure 3c). Figure 2: Catalase (CAT) activity (nmol-min\({}^{-1}\)-mg\({}^{-1}\) protein, mean \(\pm\) SD) in _S. senegalensis_ muscle (**a**), liver (**b**), and brain (**c**) after 28 days of Hg exposure. White bars represent non-contaminated treatments (non-CONT) and gray bars represent Hg-contaminated treatments (CONT). Control (CTR)—seawater temperature set at 19 \({}^{\circ}\)C and pH set at 8.0 units; A—seawater temperature set at 19 \({}^{\circ}\)C and pH set at 7.6 units; W—seawater temperature set at 23 \({}^{\circ}\)C and pH set at 8.0 units; A + W—seawater temperature set at 23 \({}^{\circ}\)C and pH set at 7.6 units. Different small letters denote significant differences between non-CONT treatments (ANOVA, \(p\) \(<\) 0.05). Different capital letters denote significant differences between CONT treatments (ANOVA, \(p\) \(<\) 0.05). Asterisks (*) represent differences between non-CONT and CONT for the same conditions (Student’s \(t\)-test: * \(p\) \(<\) 0.05; ** \(p\) \(<\) 0.005; *** \(p\) \(<\) 0.0005).