The non-steroidal anti-inflammatory drug (NSAID) diclofenac is a pervasive aquatic contaminant. While its presence in water systems is well-documented, its sub-chronic impact on the fundamental energy metabolism of fish remains poorly understood. This study investigated the temporal effects of a high sublethal concentration of diclofenac sodium on the protein, lipid, and carbohydrate reserves of Nile tilapia (Oreochromis niloticus). The 96-hour median lethal concentration (LC₅₀) of diclofenac for O. niloticus was determined to be 18.5 mg/l. Based on this, fish were exposed to a sublethal concentration of 1.85 mg/l (1/10<sup>th</sup> LC₅₀) for 24, 48, 72, and 96 hours, and 7, 14, and 21 days. Tissues (gill, liver, kidney, blood) were analyzed using spectrophotometric methods to quantify concentrations of total proteins, lipids, and carbohydrates. Data were analyzed using two-way ANOVA. Diclofenac exposure induced a severe, time-dependent catabolism of essential macromolecules across all tissues. A consistent hierarchical pattern of mobilization was observed: Lipids > Carbohydrates > Proteins, indicating a strategic sacrifice of energy reserves. The kidney and liver were the most vulnerable organs, suffering near-total depletion of lipids (≥96%) and carbohydrates (≥85%), and extreme protein loss (≥77%). The gill demonstrated the most severe relative carbohydrate depletion (90.4%). Kinetic analysis revealed a biphasic response: a rapid initial depletion phase (0-96 hours) followed by a slower, chronic exhaustion phase, indicative of recovery from shock and a progression from acute stress to systemic energy bankruptcy. This study demonstrates that sub-chronic exposure to diclofenac triggers a catastrophic multi-system metabolic crisis, forcing a hierarchical mobilization of energy reserves that compromises vital physiological functions. These findings provide a mechanistic explanation for the sublethal toxicity of diclofenac and highlight a significant threat to fish health, growth, and population sustainability, underscoring the ecological risk of pharmaceutical pollutants in aquatic environments.
Keywords: Diclofenac; Oreochromis niloticus; Metabolic disruption; Energy mobilization; Sub-chronic toxicity; Aquatic toxicology.