Zahran et al. 2023 — Mercury bioaccumulation in Nile tilapia muscle under HgCl₂ exposure; Nannochloropsis dietary mitigation
This controlled aquaculture study evaluated mercury (Hg²⁺) bioaccumulation in muscle tissue of Nile tilapia (Oreochromis niloticus) exposed to a sub-lethal concentration of HgCl₂ (0.3 mg/L; ¼ LC₅₀) for 21 days, and assessed whether dietary supplementation with Nannochloropsis oculata microalga (5% or 10% of feed) could reduce Hg muscle deposition. Hg²⁺ toxicity led to significant musculature bioaccumulation, inhibited acetylcholinesterase (AChE) activity, downregulated antioxidant- and stress-related genes, and caused histopathological changes in gills and intestine. Supplementation with 10% N. oculata upregulated antioxidative genes, downregulated stress-apoptotic genes, and produced minor to no histopathological lesions. The study quantifies Hg accumulation in the muscle of a globally consumed aquaculture fish species under controlled contamination conditions and demonstrates a dietary mitigation strategy.
Key numbers
- n = 120 Nile tilapia; 4 groups × 3 replicate tanks × 10 fish/tank (10 fish/tank)
- Hg exposure: 0.3 mg/L HgCl₂ (sub-lethal, = ¼ LC₅₀ = 1.21 mg/L at 96h)
- Duration: 21 days
- Hg²⁺ bioaccumulation in muscle tissue: significantly elevated in Hg-exposed groups vs. control; specific concentration values in source tables
- N. oculata 10% diet lowered Hg residues in muscle; N. oculata 5% less effective
- AChE activity significantly inhibited by Hg exposure; restored by dietary N. oculata
- Histopathological changes in gills and intestine reduced/eliminated by 10% N. oculata
- 96h LC₅₀ for Hg in Nile tilapia: 1.21 mg/L
- Study conducted at Aquatic Animal Medicine Laboratory, Mansoura University, Egypt
- Journal: Environmental Science and Pollution Research
Methods (brief)
Static-renewal aquarium system with daily HgCl₂ dosing (1000 mg/L stock, diluted to 0.3 mg/L). Three tissues assayed for Hg but muscle is the food-relevant matrix. Antioxidant and stress-gene expression (RT-PCR); histopathology. AChE activity measured in serum. Egypt (Mansoura University).
Implications
Certification: Nile tilapia muscle accumulates measurable Hg under simulated aquaculture contamination conditions; tilapia is one of the most globally consumed aquaculture species and a relevant food-safety matrix for Hg. Courses: Demonstrates dose-dependent Hg accumulation in a commercial food fish species; dietary microalgae as a novel mitigation approach in aquaculture is a timely emerging topic. App: Tilapia from aquaculture settings with water quality risks should carry Hg flags; mitigation via feed additives is not yet standard practice and cannot be assumed. Microbiome: Not applicable.