Persistent organic pollutants, lipid remodeling and gene expression during reproductive maturation in Atlantic cod (Gadus morhua)

• POP levels were highest in liver and lowest in muscle, testicular tissue and larvae. • Triacylglycerol, phospholipids and n-3 PUFA had higher levels in ovaries compared to testes. • Increase in ovarian lipids concurs with an increase of lipases gene expression. Environmental contaminants pose a significant risk to marine species due to their persistence, bioaccumulation, and potential to impair reproduction. In fish, persistent organic pollutants (POPs) are primarily acquired through diet. This study investigated POP accumulation and lipid metabolism in farmed Atlantic cod ( Gadus morhua ) from early maturation to spawning, integrating chemical analyses with gene expression profiling of lipid- and stress-related pathways. Polychlorinated biphenyls (PCBs) were the most abundant POPs detected, followed by toxaphene, reflecting feed composition. POP concentrations were highest in liver and whole body, lower in gonads and muscle. Maturation was associated with sex-specific changes in gonadal lipid composition, including increased free fatty acids and cholesterol in males, and elevated n-3 polyunsaturated fatty acids in females. In the liver, oxidative stress-related genes (e.g., cat ) and lipid metabolism genes (e.g., acly ) were downregulated, particularly in females. Lipases involved in extracellular uptake ( lpl ) and intracellular hydrolysis ( lipe-2 ) were downregulated in liver and upregulated in gonads. These findings demonstrate that POP accumulation, lipid remodeling, and gene expression are dynamically influenced by reproductive maturation in Atlantic cod.