Enrichment in ω3 of Hermetia illucens prepupae of from oilseed co-products

Belgian fish farmers from the Walloon region are currently looking for alternative feed sources as they mainly produce rainbow trout, a carnivorous species with high protein and lipids requirement. Among the available new feed sources, Hermetia illucens (L. 1758) is a promising insect species with a polyphagous diet, a fast larvae growth rate and a short life cycle. Moreover, several studies have shown that the larvae composition in macronutrients is function of their diet and could be manipulated. The current compo-sition of H. illucens larvae is characterized by a high-saturated fatty acids level (± 76%) with mainly lauric acid (± 55%) and do not meet the nutritional requirements of trout. The objective of this study was to adjust the profile in polyunsaturated fatty acids of H. illu-cens larvae by manipulating their diets. Nevertheless, the legislation governing insect rearing is constantly evolving but remains restrictive concerning the allowed feed ingredi-ents for insect development. Consequently, this study focused on diet formulation from local plant co-products to reduce the ecological footprint of insect and fish productions. Considering the seasonality and low-fat content of the co-products, the diet formulations were supplemented with oilseed meal cakes. An experimental rearing has been devel-oped and nutrition tests were conducted. After selecting populations (100 individu-als/population) of young H. illucens larvae (± 0.01 g), different diets enriched with flax and two rapeseed meal cake (chemical vs mechanical extraction) were tested in a con-trolled environment (60% relative humidity - 27 °C). Six incorporation rates per meal cake (10 - 20 - 40 - 60 - 80 - 100%) were tested in triplicate (n = 3). The larvae were col-lected at prepupal stage and each population were lyophilized and cold ground into flour. Lipids from prepupae flours were extracted by Folch's method while fatty acids have been esterified and analyzed by gas chromatography. Protein and ash levels were also quantified respectively by Dumas’ method and combustion. The proportions between saturated fatty acids (SFA) and unsaturated fatty acids (UFA) were specifically evaluat-ed as well as the percentage of α-linolenic acid (ALA - C18: 3Ꙍ3). The incorporation of meal cake has reduced the ratio SFA/UFA from 4.11 to 1.44 and increased ALA per-centage from 0.72 to 15.83. The increase in the proportion of UFA in H. illucens prepupae flour should allow an increase of their incorporation in artificial diets for rainbow trout.