Black soldier fly larvae oil as an alternative lipid source in diets for gilthead seabream (Sparus aurata) juveniles

The black soldier fly (Hermetia illucens, HI) is a promising insect species to be included in aquafeeds. HI larvae are rich in protein but also in fat, with a fatty acid profile dominated by saturated and medium-chain fatty acids. This study aimed to evaluate the replacement of vegetable oils (VO) with HI larvae oil (HIO) and its effects on growth, whole-body composition, nutrient retention, diet digestibility, and digestive enzyme activity. A control diet (HIO0, 45% crude protein, 18% lipids) was formulated to include 9.5% of a VO blend, and three other diets were formulated similar to the control but with the VO blend replaced at 42% (HIO42), 84% (HIO84), and 100% (HIO100). A growth trial was performed with triplicate groups of fish (initial body weight of 63 g) hand-fed to apparent visual satiation for 10 weeks. A digestibility trial was also performed simultaneously with triplicate groups of fish with similar initial body weights. Results indicate that the total replacement of VO mix with HIO did not affect growth performance, but feed efficiency and protein efficiency ratio linearly improved with the increase of HIO in the diets. No differences between groups were found in whole-body composition and protein and energy retention. There was a trend for protein and energy digestibility to linearly increase with dietary HIO inclusion. Lipid digestibility was not affected by diet composition, however, the apparent digestibility of saturated fatty acids increased and of unsaturated decreased with the increase of dietary HIO inclusion. Total proteases activity was higher in fish fed diet HIO84 and lipase activity followed a positive linear trend with the increase in dietary HIO content. Overall, present results indicate that gilthead seabream can effectively utilize HIO without compromising growth performance and digestibility while improving feed utilization efficiency, thus establishing its potential as an alternative lipid source for aquafeeds.