Short-Term Exposure to Tebuconazole Triggers Haematological, Histological and Biochemical Disturbances in Rainbow Trout (Oncorhynchus mykiss)

Abstract

Tebuconazole (TBZ), a triazole-class fungicide widely used in agriculture, is frequently detected in aquatic environments due to runoff and leaching, where it poses a threat to non-target aquatic organisms. This study investigates the acute toxicity of TBZ on juvenile rainbow trout (Oncorhynchus mykiss), a commercially important cold-water fish species. The 96 h LC₅₀ value was determined to be 9.05 mg/L using probit analysis. In addition to mortality, the physiological responses of fish exposed to both LC₅₀ and maximum tolerance concentration (MTC; 6 mg/L) were evaluated through haematological and histological assessments. TBZ exposure significantly suppressed key haematological parameters, particularly WBC, RBC, HGB, HCT, and LYM, indicating immunosuppression and potential hypoxia. Histological examination revealed progressive and regressive damage in gill tissues, including epithelial lifting, hyperplasia, and hypertrophy, which were more severe in the LC₅₀ group. These alterations were quantified using a semi-quantitative scoring system. Additionally, significant changes in biochemical parameters such as ALT, AST, creatinine, total protein, and glucose levels were observed, further indicating hepatic and renal dysfunctions induced by TBZ exposure. The findings demonstrate that TBZ exposure induces substantial physiological and structural impairments in rainbow trout, highlighting the importance of assessing the ecological risks of fungicide contamination in aquatic environments. The study also provides a dose-response model that can be used to estimate mortality risk in aquaculture operations exposed to TBZ.

Keywords: acute toxicity; haematological parameters; rainbow trout; tebuconazole (TBZ).

Figure 1

Dose–response curve (Log₁₀-transformed) of rainbow trout following exposure to varying concentrations of tebuconazole.

Figure 2

Histological observation of gill in control, MTC and LC₅₀ groups. (A): Control, (B): MTC and (C): LC₅₀. Histological symptoms are shown with arrows (red: hyperplasia, yellow: hypertrophy, green: epithelial lifting).

Figure 3

Plasma biochemical parameters measured in Control, MTC, and LC₅₀ groups. Different letters (a, b, c) above the bars denote statistically significant differences among groups (p < 0.01).