Tissue-specific responses of Thiamethoxam treatment in rainbow trout (Oncorhynchus mykiss)

This study was carried out to evaluate the findings of oxidative stress-mediated hemotoxicity, hepetotoxicity and nephrotoxicity in rainbow trout (Oncorhynchus mykiss) caused by Thiamethoaxam, a neonicotinoid. For this purpose, 96 rainbow trout (165.35±30.15 g and 20.55±1.16 cm) were used in 3 replicates with 8 fish in each group. In the study, 4 groups were formed as control and 3 different doses of Thiamethoxam (25 mg/l, 75 mg/l, 125 mg/l). At the end of the experimental period, blood taken from all groups was used for hematologic analysis and tissues were used for pathologic evaluation. As a result of thiamethoxam administration, hepatosomatic index, one of the biosomatic index indicators, decreased in the 25 and 75 mg/l dose groups and increased in the 125 mg/l group compared to the control group. In terms of hepatosomatic index, only the 125 mg/l Thiamethoxam group, which was the highest application dose, was statistically different from the other two Thiamethoxam application doses (25 mg/l and 75 mg/l) (p<0.05). At the end of the study, the rate of weight gain (%) compared to the initial weights decreased with increasing Thiamethoxam dose compared to the control group. The amount of urea and uric acid in blood serum shows an increase compared to the control group. In 75 and 125 mg/l groups, urea content is statistically different from the control and 25 mg/l Thiamethoxam groups (p<0.05). There is a significant difference between 125 mg/l Thiamethoxam group and control group in terms of uric acid content (p<0.05). The amount of MDA, an indicator of lipid peroxidation, increased in parallel with the increase in Thiamethoxam dose compared to the control group. GSH-Px, one of the important enzymes of the antioxidant system, decreased in parallel with the increase in Thiamethoxam doses used and the difference between the high application doses (75 and 125 mg/l) and the control group was significant (p<0.05). Histopathologic examinations showed that the liver tissue was normal in the control group and close to normal in the 25 mg/l Thiamethoxam group. In the 75 and 125 mg/l Thiamethoxam groups, degeneration in hepatocytes, necrosis areas in the parenchymal region, congestion, steatosis, vacuolar degeneration and hepatocellular degeneration in the parenchymal region, degeneration and proliferation in the bile duct were observed. In the kidney tissue, while normal structure was observed in the control group, a small amount of tubule epithelial degeneration and glomerular atrophy were observed in the 25 mg/l Thiamethoxam group. In 75 and 125 mg/l Thiamethoxam groups, glomerular atrophy, hydropic degenerations in tubules, necrosis, decrease in hematopoietic tissue, increase in melanomacrophage centers, separation from basal lamina in tubule epithelium were detected as similar lesions. It was understood that Thiamethoxam, which is widely used in agricultural activities, causes oxidative stress in the organism it is in contact with as a result of its participation in the ecosystem inhabited by other organisms other than the target organisms, depending on the dose exposed, negatively affects the oxidant / antioxidant system balance and has effects that may cause lesion formation in tissues.