Full-fat black soldier fly larvae (Hermetia illucens) meal and paste in extruded diets for Atlantic salmon (Salmo salar): Effect on physical pellet quality, nutrient digestibility, nutrient utilization and growth performances

The present study investigated the effect of graded levels of black soldier fly larvae (BSFL) (Hermetia illucens) meal and paste on physical pellet quality, digestibility and utilization of nutrients and growth performances in extruded diets for Atlantic salmon (Salmo salar). A total of 1260 Atlantic salmon with 34 g of mean initial weight were randomly distributed into 21 fiberglass tanks and fed with one of seven isonitrogenous, isolipidic and isoenergetic diets for seven weeks. The experimental diets consisted of a control diet based on fishmeal, soy protein concentrate, corn gluten, faba bean and fish oil (Control-1); three diets with increased levels of full-fat BSFL meal, substituting 6.25% (6.25IM), 12.5% (12.5IM) and 25% (25IM) of the protein content of Control-1; two diets with increased levels of full-fat BSFL paste, substituting 3.7% (3.7IP) and 6.7% (6.7IP) of protein from Control-1 and an extra control diet with 0.88% of formic acid (Control-2). Pellet durability and hardness were overall high for all diets. However, the expansion, sinking velocity and water stability of feed pellets were lower with increased inclusion of BSFL meal and paste. Dietary inclusion of BSFL meal or paste did not affect the feed intake of fish. Further, replacing the protein content of the control diet with up to 12.5% and 6.7% of BSFL meal and paste, respectively, did not compromise fish growth rate or feed conversion ratio, although polynomial contrast analysis showed that increasing BSFL meal level in the diet linearly (p < .05) decreased these parameters. However, apparent digestibility coefficient (ADC) of protein and lipid, protein efficiency ratio and lipid retention were reduced linearly (p < .05) with increasing inclusion level of BSFL meal. Further, increasing dietary levels of BSFL paste linearly (p < .05) reduced ADC of protein, protein efficiency ratio and phosphorous retention. Despite the decreased ADC of protein, protein retention was not compromised by the inclusion of BSFL meal or paste. Replacement of 25% of dietary protein with BSFL meal decreased (p < .05) growth rate, accompanied by lower (p < .05) ADC and utilization of lipids and protein efficiency ratio. The present study showed that BSFL meal and paste could replace up to 12.5% and 6.7% of dietary protein, respectively, without compromising growth performance in Atlantic salmon.