Evaluation of Chromium Stress in Nile Tilapia: Insights Into Haemato‐Biochemical and Physiological Alterations

Chromium in its hexavalent form (Cr⁶⁺) is highly toxic and widely recognized for its persistence and bioaccumulative potential in aquatic ecosystems. Despite extensive reports on chromium toxicity, information on its integrated physiological, biochemical and enzymatic impacts on widely cultured fishes remains limited. The present study evaluated both acute and sublethal effects of chromium on Nile tilapia (Oreochromis niloticus), an ecologically and commercially important fish species. The results of the acute toxicity testing revealed a 96-h LC₅₀ value of 49.40 mg L^-1. During the 30-day sublethal trial, significant (p < 0.05) alterations in haematological parameters were recorded, including 28%-40% reductions in RBC, haemoglobin and haematocrit, along with an increase in WBC, indicating anaemia and stress-induced immune activation. Serum biochemical results showed a 40%-45% rise in glucose levels and a significant decline in total protein and albumin (p < 0.05), reflecting metabolic stress and impaired liver function. Digestive enzyme activities were inhibited, with protease, amylase and lipase decreasing by 10%-35%, suggesting impaired nutrient digestion and assimilation. Physiological indices, including HSI and GaSI, decreased by over 50%, whereas specific growth rate (SGR) indicated negative values, demonstrating suppressed growth and reduced energy utilization. Collectively, these findings provided mechanistic evidence that chromium toxicity induces haematological alterations, leading to impaired oxygen transport, metabolic imbalance and reduced digestive efficiency in O. niloticus. These results also highlighted the ecological risk of chromium contamination in freshwater systems and emphasize the need for stricter regulation of metal discharge to safeguard aquatic biodiversity and aquaculture productivity.