Effect of two full-fat insect meals, yellow mealworm and black soldier fly larva, on growth performance of juvenile yellowtail

Abstract Given the expanding demand for fish meal (FM) worldwide, insect meal has become a promising alternative to FM for sustainable aquaculture. Yellowtail ( Seriola quinqueradiata ), the predominant farmed fish in Japan, is a carnivorous marine species that requires a substantial quantity of FM in its diet. Two feeding trials were conducted with the aim of assessing the applicability of two full-fat insect meals, yellow mealworm ( Tenebrio molitor ) meal (TM) and black soldier fly ( Hermetia illucens ) larvae meal (HI), as FM substitutes in for juvenile yellowtail. In the first trial, replacing 24.3% of FM with TM resulted in a final fish weight of 137.4 ± 40.1 g (mean ± SD as also indicated for subsequent values), comparable to the control group with a weight of 139.5 ± 44.0 g, while maintaining an equivalent level of n-3 fatty acid content across all diets used in the trial. The body weight of fish fed a diet containing HI, at 121.2 ± 31.0 g, was significantly lower than the control group, whereas the difference between fish fed a diet containing TM was not statistically significant. According to the growth analysis, dietary inclusion of TM was more suitable than that of HI, prompting a second trial to evaluate the maximum limit of FM substitution with TM without adjusting fatty acid profiles across diets. In the subsequent trial, fish growth exhibited a clear decrease trend with the inclusion rate of TM. These findings suggest that, while the substitution of FM with HI and TM has been shown to be feasible under equivalent fatty acid profiles in diets, the imbalanced fatty acid profile resulting from the inclusion of full-fat insects could be attributed to a deficiency in n-3 fatty acids, leading to the observed growth retardation in juvenile yellowtail.