Production Performance, Nutrient Digestibility, Serum Biochemistry, Fillet Composition, Intestinal Microbiota and Environmental Impacts of European Perch (Perca Fluviatilis) Fed Defatted Mealworm (Tenebrio Molitor)
Authors: Tran Hung Quang , Prokešová Markéta , Zare Mahyar , Matoušek Jan , Ferrocino Ilario , Gasco Laura , Stejskal Vlastimil 
Published: July 2021

Abstract
Background: Yellow mealworm (Tenebrio molitor) larvae meal (TM), one of seven approved insect species used in aquafeeds, is a frequently investigated candidate for fish diets. Results: This study aimed to investigate the effects of dietary defatted TM on production performance, serum biochemistry, nutrient digestibility, fillet traits, intestinal microbiota, and environmental impacts of perch (Perca fluviatilis). Four experimental diets, characterized by defatted TM inclusion levels of 0, 6.8, 13.5 and 20.3%, respectively, or 0, 25, 50, and 75% at the expense of fishmeal (TM0, TM25, TM50, and TM75, respectively) were fed to juvenile perch (bodyweight 20.81 ± 3.36 g, total length 117.7 ± 7.2 mm) (quadruplicated per diet) for 105 days. Inclusion levels of 6.8% or 25% fishmeal replacement by defatted TM did not show a significant effect on specific growth rate and feed conversion ratio (P > 0.05), while further levels of 13.5 and 20.3%, or 50 and 75% fishmeal replacement with defatted TM, respectively, displayed a significant delay in these indices compared to the control diet (P < 0.001). The aspartate aminotransferase activities in perch’s serum increased with increasing dietary TM (P = 0.044). Nutrient digestibility of perch exhibited TM-dose dependent (P < 0.05). Dietary defatted TM did not lead to any significant changes in the fillet composition of perch (P > 0.05). Defatted TM did not modify diversity of fish gut microbiota (Chao1 index, P = 0.742; Shannon index, P = 0.557; and observed species, P = 0.522), but significantly reduced abundance of Lactobacillus (P = 0.018) and Streptococcus (P = 0.013) while fed TM75 relative to TM0. TM-containing diets generated a comparable amount of total solid waste and solid phosphorus waste with TM0, except TM25, whereas solid nitrogen waste significantly increased with elevated TM levels (P < 0.001). Perch fed TM25 was comparable with TM0 for global warming potential, acidification, and land use (P > 0.05), whereas TM50 and TM75 exerted heavier burdens on energy use, eutrophication, and water use than TM0 (P < 0.001). Fishmeal replacement by TM significantly reduced economic fish-in fish-out (P < 0.001).Conclusion: The inclusion of 6.8% or 25% fishmeal replacement by defatted insect meal (T. molitor) in European perch diets resulted in comparable production performance but entailed heavier burdens associated with solid outputs waste and environmental impacts. The present study underlined the major bottleneck of a substantial inclusion of defatted insect meal (T. molitor) in fish diets associated with solid nitrogen waste and environmental consequences associated with one unit of farmed perch produced. Our multidisciplinary study suggested important aspects while formulating diets for fish, using insect meals regarding production performance and environmental issues.