## 4 Discussion  
Fish respond to stress by activating the neuroendocrine system that leads to changes in plasma and tissue ion and metabolite levels, hematological profile, and HSPs [23]. Biochemical and hematological analyses thus provide important information about secondary response to stress in wild and captive conditions [6; 24; 25]. The GLU, TRIG, CHOL, and TP levels can reflect both the nutritional status and metabolic responses of fish to stress, since they represent the energy available during exposure to stressful conditions [23; 26; 27]. Our study has shown no significant difference in GLU level between examined groups, suggesting that GLU was not affected by farming condition and handling stress, which is consistent with results obtained by [PERSON] et al. [17] and [PERSON] et al. [28], but opposite to those of [PERSON] et al. [5], who reported a significant elevation of GLU in farmed _Dicentrarchus labrax_ compared to their wild counterparts. Continuous availability of high-energy feed (relatively high protein, lipids, and carbohydrates) and the reduction of activities in the culturing environment [29] resulted with significantly higher TRIG and TP concentrations, including ALB and GLOB fractions in farmed turbot. A wide range of GLU and TP observed in the wild-caught group (0.05-16.4 mmol/L and 10-46 g/L, respectively), combined with generally decreased other energy metabolites (TRIG), indicate possible starvation that is frequent in wild populations and could also be caused by _Bothirocephalus scopii_ detected in the wild-caught turbot intestine. \(B\). _scorpii_, the most common parasite in turbot [30], causes a progressive intestine necrosis and atrophy, leading to malnutrition and lower resistance to stress [31] that could be the reason for significantly higher A/G ratio, which is often used as an indicator of stress response [27]. Reduction in plasma TRIG levels in the wild-caught fish could be attributed to lipolysis during starvation [32]. CHOL concentrations did not differ significantly between examined groups, which is in line with [PERSON] et al. [33], who also did not record significant differences between farmed and wild turbot populations. [PERSON] [34] reported that CHOL concentration increases as the fish size increases. However, we did not record such correlation (data not shown). Urea and creatinine are end-products of protein metabolism, and changes in their concentrations could be caused by liver, kidney, or gill osmoregulatory distinction [35; 36; 37]. We observed morphological changes in gill tissue of both groups (Figure 3A,B) but URE levels were not significantly different. However, manifold-higher CRE levels in the farmed group indicate disturbance of kidney filtration process, which is corroborated by detected  
Figure 3: Histopathological changes in tissues of the wild-caught ((**A**)—gills; (**C**)—caudal kidney; (**E**)—liver; (**G**)—intestine; (**I**)—spleen) and the farmed ((**B**)—gills; (**D**)—caudal kidney; (**F**)—liver; (**H**)—intestine; (**J**)—spleen) turbot _Scophthalmus maximus_. pathohistological changes (Figure 3D). [PERSON] et al. (2018) and [PERSON] (2018) also stated that increased CRE concentrations suggest insufficiency of the kidney excretory functions. Significantly elevated TBIL levels in the farmed turbo in relation to its wild counterparts may indicate liver damage ([PERSON] et al., 2018). Histological analysis of the wild-caught turbid liver (Figure 3E) exhibited scarce accumulation of glycogen with densely packed hepatocytes, indicating lower metabolic activity, while the farmed turbo liver showed hepatocytes with increased accumulation of lipids and glycogen. Plasma concentration of the electrolytes, such as Ca and P, have been used as indicators of secondary phase of stress response in fish, and their changes can be related to pathological disturbances ([PERSON] et al., 2018; [PERSON] et al., 2018).