Document Type : Research Paper
Authors
1
Department of Pathology and Clinical Pathology, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran
2
Department of Aquatic Animal Health, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran
3
Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran
4
Department of Comparative Bioscience, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran
Abstract
Heavy metal pollution, particularly from mercury, poses a significant threat to aquaculture sustainability and food safety. This study investigated the protective efficacy of dietary thymol, curcumin, and menthol against mercuric chloride (HgCl₂)-induced gill histopathology in common carp (Cyprinus carpio). A total of 240 fish (50 ± 2 g) were distributed in a completely randomized design into eight treatments for 8 weeks: Control, Hg (0.44 mg/L HgCl₂ in water), Thymol (100 mg/kg feed), Curcumin (15 g/kg feed), Menthol (2.5 g/kg feed), and three co-exposure groups (Hg+Thymol, Hg+Curcumin, Hg+Menthol). Histopathological examination revealed severe lymphoplasmacytic proliferative branchitis, necrosis, and lamellar destruction in the Hg group. Thymol supplementation demonstrated the most potent protective effect, reducing lesions to mild branchitis and edema. Curcumin provided moderate protection, notably mitigating the severity of the injury. Conversely, menthol failed to alleviate mercury-induced pathology and, when administered alone, induced mild branchitis and aneurysms. The results indicate that the protective effects of these phytochemicals are compound-specific. Thymol is highly effective in preventing HgCl₂-induced gill damage, curcumin offers significant but moderate protection, while menthol is ineffective and potentially irritating at the tested dose. Thymol is recommended as a promising dietary supplement for enhancing carp resilience in mercury-contaminated aquaculture environments.
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