Combined effects of thermal stress and benzene or toluene exposure on the immune and reproductive disruption in Nile tilapia (Oreochromis niloticus)

Abstract

Thermal stress and exposure to benzene or toluene frequently co-occur in aquatic environments; however, information on their combined effects on fish physiology remains limited. Therefore, this study examines the interactive impacts of high temperature and benzene or toluene exposure on the immune and reproductive systems of Nile tilapia (Oreochromis niloticus). Fish were assigned to six experimental groups: the first group served as the control (29 ± 1 °C), the second group was exposed to thermal stress (34 ± 1 °C), the third and fourth groups were exposed to benzene (6.1 mg/L) and toluene (5.9 mg/L), respectively, at 29 ± 1 °C, and the fifth and sixth groups were exposed to benzene (6.1 mg/L) and toluene (5.9 mg/L), respectively, at 34 ± 1 °C. All treatments were conducted over a two-week period. The findings showed that combined exposure caused greater immunological and reproductive alterations than individual stressors, with more pronounced decreases in lysozyme (LYZ), immunoglobulin M (IgM), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone (T) levels, and greater increases in interleukin-1 beta (IL-1β) and interleukin-6 (IL-6) concentrations. Histopathological examination revealed severe splenic lesions, including necrosis, vascular changes, and hemosiderin deposition, together with severe testicular damage characterized by seminiferous tubule degeneration and complete atrophy of sperm cells, accompanied by greater fibrosis in both organs compared with the individual stressor groups. These findings indicate that the combined effects of elevated water temperature and benzene or toluene contamination may compromise immune competence and reproductive capacity in fish, highlighting potential risks to aquatic populations under ongoing environmental change.