This study investigated the comparative bioaccumulation and induced toxicity of lead (Pb) and nickel (Ni) in grass carp (Ctenopharyngodon idella). Healthy fish (7-8 cm; 60-70 g) were acclimatized for 7 days in 80-L glass aquaria and then divided into control and treatment groups (n = 3 fish/group for each exposure concentration). The treatment groups were exposed to varying concentrations of lead acetate (Pb acetate) and nickel chloride (NiCl₂) over specified durations. For acute toxicity assays, fish were exposed to NiCl₂ at concentrations of 6.0 mg/L for 24 hours, 5.0 mg/L for 48 hours, and 4.6 mg/L for 72 hours, while Pb acetate exposure concentrations were 5.0 mg/L for 24 hours, 4.8 mg/L for 48 hours, and 4.6 mg/L for 72 hours. In contrast, chronic exposure involved lower concentrations of NiCl₂ (4.0 mg/L for 10 days, 3.5 mg/L for 20 days, 3.0 mg/L for 30 days, 2.5 mg/L for 45 days, and 2.0 mg/L for 60 days) and Pb acetate (3.5 mg/L for 10 days, 2.5 mg/L for 20 days, 2.0 mg/L for 30 days, 1.5 mg/L for 45 days, and 1.0 mg/L for 60 days). The results showed significant hematological and biochemical changes, including decreased hemoglobin (4.96±0.876 g/dL) and white blood cell count (94.43±30.291 cells/μL) in nickel-exposed fish. Biochemical assessments revealed increased glucose levels, fluctuating urea and creatinine profiles, and decreased Ca2+ serum levels. Tissue-specific bioaccumulation was observed, with considerable accumulation in liver tissues. The findings highlight the potential risks associated with heavy metal concentrations in aquatic ecosystems and underscore the need for monitoring and regulating heavy metal levels to protect aquatic life and ensure food security.