Growth performance of rainbow trout fed defatted black soldier fly meal:preliminary results

Introduction: The search for alternative protein sources is an ongoing problem for aquaculture sustainability. This is essentially due to the contemporary increased demand and decreased availability of fish meal (FM), being responsible for price increase of aqua feed. In order to face this problem, researches have been focusing on insect meals, with some results highlighting that they can be profitably used in fish diets (Barroso et al., 2014; Henry et al., 2015). Black soldier fly (Hermetia illucens) larvae meal (HIM) could be an interesting choice due to its favorable nutritional profile. Aim of this trial was to investigate the effects of the inclusion of a defatted HIM in rainbow trout diets on animal growth performance and nutrient digestibility. Material and methods: 360 rainbow trout (Oncorhyncus mykiss) were individually weighed and allotted in 3 groups (4 tanks/group). Each group was fed a different diet (HIM0, HIM25, HIM50). The diets were isonitrogenous and isoenergetic, and contained 0, 20 and 40% of defatted HIM leading to a substitution of 0, 25 and 50%, FM. The trial lasted 78 days and the fish were fed 7 days a week at 1.5% of body weight. Individual mean weight gain (WG), feeding rate (FR), feed conversion rate (FCR), protein efficiency ratio (PER), and specific growth rate (SGR) were determined using the tank as experimental replicate. At the end of the trial, hepatosomatic (HSI) and viscerosomatic (VSI) indexes as well as fatness coefficient (CF) were evaluated on 20 fish per treatment. Data were analyzed by one-way ANOVA and significance was declared at P<=0.05. Results and discussion: Growth parameters did not show significant differences among groups. Individual mean WG and FR ranged from 358.93 to 366.53g and from 1.39 to 1.41%, respectively. FCR was lower than 1 for all groups. The average results were about 2.44 and 1.40% for PER and SGR, respectively. No significant differences were recorded for somatic indexes and fatness coefficient. HSI ranged from 1.63 to 1.73% while VSI from 8.94 to 9.25%. Overall, the results are in line with data reported in literature. Conclusion: Up to a level of 50%, the substitution of FM with HIM led to modification of neither growth performance nor somatic indexes of rainbow trout. This is undoubtedly an interesting result in a view to seek for innovative feedstuffs for carnivorous fish diets. References: Barroso, F.G., de Haro, C., Sanchez-Muros, M.J., Venegas, E., Martinez-Sanchez, A., Perez-Banon, C., 2014. The potential of various insect species for use as food for fish. Aquaculture, 422-423: 193-201. Henry, M., Gasco, L., Piccolo, G., Fountoulaki, E., 2015. Review on the use of insects in the diet of farmed fish: past and future. Anim. Feed Sci. Tech., 203: 1-22.