The potential of insects as alternative ingredients in animal feeds is well-established. However, limited information is available on the use of insect oils as alternative lipid sources in aquafeeds. To address this, a study was conducted on gilthead seabream (Sparus aurata) juveniles to evaluate the effects of including black soldier fly (Hermetia illucens) larvae oil (HIO). Diets were formulated to include 4, 7.9, and 9.5 % HIO, replacing a vegetable oil blend at 42, 84, or 100 %, respectively. After 70 days, the effects on liver fatty acid profiles, plasma metabolites, and lipid metabolism gene expression were assessed. The results showed that HIO inclusion led to a linear decrease in plasma lipids and triglycerides, while high-density lipoprotein levels increased. The experimental diets also altered the liver's fatty acid composition without affecting total lipid content. There was an increase in the liver's saturated fatty acid content, like lauric acid, and monounsaturated fatty acids, like oleic acid. In contrast, n-3 and n-6 polyunsaturated fatty acid content was reduced, although EPA and DHA levels remained unaffected. Additionally, the content of C16:0 and C18:0 (% of total fatty acids) was higher in the liver than in the corresponding diets. The inclusion of HIO had minimal impact on the expression of genes associated with fatty acid synthesis, transport, and β-oxidation. However, a downregulation of elongation of very long-chain fatty acids proteins 6 and 1b (elovl6 and elovl1b) was observed with increasing HIO levels. Overall, the study indicates that up to 9.5 % HIO inclusion in diets is well tolerated by gilthead seabream juveniles, with minimal effects on plasma metabolites and key gene expression related to fatty acid metabolism. These findings support the use of HIO as a viable alternative lipid source for juvenile gilthead seabream, contributing to the sustainable development of aquafeeds.