Abstract
Background:
The marine environment is threatened by heavy metal accumulation, which can build in fish tissues and affect human consumption. Differences in fish species metabolism and habitat may alter proximate composition and the degree of heavy metal accumulation.

Aim:
This study evaluated the proximate composition (lipid and protein composition) and accumulation of cadmium (Cd), lead (Pb), and mercury (Hg) in selected fish species collected from different depths along the Tripoli coastline.

Methods:
A total of 56 fish samples representing Marbled spinefoot (Siganus rivulatus), Salema (Sarpa salpa), Dusky grouper (Epinephelus marginatus), and Stargazer (Uranoscopus scaber) were analyzed. Crude protein was measured using a DR3900 spectrometer, and lipid was analyzed using Soxhlet extraction. Mercury (Hg), cadmium (Cd), and lead (Pb) were digested using a microwave digestion system followed by a Cold Vapor Atomic Absorption Spectroscopy (CV-AAS) system for mercury and a Graphite Furnace AAS (GFAAS; novAA800) for lead and cadmium.

Results:
Statistically significant differences in lipid and crude protein contents were observed between coastal and deep-sea species (t-test, p ˂ 0.001), with deep-water demersal species revealing higher lipid and protein levels. Uranoscopus scaber exhibited the highest mean concentrations of selected heavy metals (lead: 0.3 mg/kg, cadmium: 0.04 mg/kg, mercury : 0.034 mg/kg), although the observed differences in heavy metal accumulation across species and all measured levels in muscle remained within permissible limits. The spatial variation analysis revealed no significant differences in the concentrations of heavy metals across the selected sampling locations. Mercury accumulation was correlated with changes in lipid and protein content among all species (p < 0.05), whereas the effects of cadmium and lead varied across species.

Conclusion:
This study provides valuable scientific insights for future environmental monitoring programs to ensure food safety and enhance the understanding of contamination dynamics along the Tripoli coast. All the fish species under study revealed levels of heavy metals within safety limits, indicating that they are considered safe for public consumption.

Key words: Crude protein; Deep-water; Food safety; Heavy metals; Lipid.