Heavy metal accumulation and biomarker responses of Nile tilapia from a coal void reservoir cage aquaculture system

• Higher levels of heavy metals in the tissues of tilapia reared in coal void cage system was observed. • Haemato-immunological parameters and inflammatory cytokine genes modulation act as reliable bio-indicator. • Histopathological alteration of liver and gill acts as bio-indicator to measure health status of O. niloticus . • Effective environmental management to mitigate the impact of metal toxicity is required to promote cage culture of tilapia. Coal mining is one of the most significant mining operations in India. Post-mining activities, often result in abandoned sites known as coal voids. Water accumulated in coal void reservoirs undergoes substantial changes in physico-chemical and biological characteristics due to heavy metal contamination. Tilapia ( Oreochromis niloticus ) with an average weight of 254.50 ± 17.65 g was randomly collected from established cage cultures in two reservoirs: Ramgarh coal void reservoir (test) and Getalsud reservoir (control) in Jharkhand, India. The objectives of the study were to delineate the effects of heavy metal exposure on hemato-immunological, biochemical, molecular, and histopathological responses in fish. The heavy metal assessment of the tilapia tissues revealed that the test group had significantly higher levels of Cr, Ni, As, Se, Pb, Zn, and Fe than the control group collected from Getalsud reservoir. Similarly, higher level of Cr, As, Pb and Fe was observed in the water sample of the test group. A significant increase in serum indices, enzymes related to oxidative stress and metabolic enzymes was observed in fish from the metal-contaminated coal void reservoir. An increasing trend in pro-inflammatory cytokine genes (TNF-α, IL-1β, and HSP-70) and downregulation of the anti-inflammatory cytokine gene (TGF-β) were observed in fish collected from coal void reservoirs. Histopathological examination of the liver and gill tissues demonstrated several deleterious alterations in coal void raised fish. The study concluded that metal contamination in coal voids profoundly affects key biomarkers of cellular, metabolic, and molecular responses in fish, indicating serious ecological and aquacultural implications.