Metabolic and Oxidative Stress Responses in Nile Tilapia (Oreochromis niloticus) During Cadmium Exposure and Recovery

Heavy metal contamination of freshwater ecosystems poses a global threat to biodiversity and food security. Cadmium, a highly toxic and persistent nonessential metal, accumulates in aquatic organisms and disrupts physiological functions and ecosystem stability. This study evaluates the chronic effects of cadmium exposure on Nile tilapia (Oreochromis niloticus) to identify integrated biomarkers for environmental monitoring. Fish were exposed to 0.1 mg·L^-1 cadmium for 40 days, followed by a 20-day recovery period. Results show that cadmium significantly reduced growth performance and feeding capacity by disrupting energy allocation. Growth inhibition was accompanied by an increased hepatosomatic ratio and reduced reproductive investment. At the sub-organismal level, cadmium induced oxidative stress, reflected by elevated catalase activity in liver and gills, while suppressing intestinal protease activity and impairing nutrient assimilation. Multivariate analyses clearly discriminated cadmium effects, confirming the consistency of biological responses. Although partial recovery was observed, persistent digestive impairment indicates lasting sublethal damage. Overall, cadmium toxicity operates through coordinated disruption of oxidative balance and metabolic efficiency. By integrating biometric, bioenergetic, and enzymatic indicators, this study provides a sensitive early-warning framework for assessing aquatic health and supports the development of environmental protection strategies.