A novel protein source from lesser mealworm (Alphitobius diaperinus) larvae meal for European perch (Perca fluviatilis): Investigation on pellet characteristics, production performance, serum biochemistry, digestibility, histology, sensory and trait of fillet, and environmental indices

The study investigated various metrics involved in the substitution of fishmeal with a novel protein source derived from lesser mealworm (Alphitobius diaperinus) larva meal (LMW) in the diets of aquaculture-emerging fish - European perch (Perca fluviatilis). Four isoprotein (50%), isolipid (14%), and isoenergy (21 MJ/kg) diets were formulated, in which fishmeal at 21% inclusion level from the control diet (CON) was replaced by LMW at 25% (LMW25), 50% (LMW50), and 75% (LMW75) and fed to European perch juveniles (body weight 36.51 ± 6.82 g) for 84 days. Graded levels of LMW significantly influenced the physical characteristics of the pellets concerning diameter, length, weight, and density (P < 0.05) but did not affect sinking velocity (P = 0.591) and expansion (P > 0.05). Analysis of post-trial serum biochemistry revealed that none of the 11 parameters investigated were affected by dietary LMW. Nevertheless, a significant difference emerged at the 24 h post-trial for phosphate (P = 0.016), total protein (P = 0.010), albumin (P = 0.026), globulin (P = 0.040), and alanine aminotransferase (P = 0.023). Dietary LMW had a positive impact on the growth performance of European perch, as evidenced by a positive linear model with specific growth rate (P = 0.002, adjusted R-squared = 0.582) and survival rate (P = 0.003, adjusted R-squared = 0.556). Examination of liver lesion severity demonstrated that fish fed the LMW75 diet exhibited less severe liver lesions than those on the CON diet (P < 0.05). Conversely, no significant observations were found regarding the intestine across the various experimental groups (P > 0.05). There was no significant difference in sensory of fish fillet fed LMW-containing diet compared to the control diet (x2-index >0.167, P > 0.05). Similarly, there were no significant differences in fillet yield and nutritional composition (P > 0.05). However, dietary LMW did have a notable impact on health-beneficial fatty acids, particularly docosahexaenoic acid and eicosapentaenoic acid, as well as total saturated fatty acids (P < 0.05). Dietary LMW significantly reduced eFIFO (P < 0.001). Including LMW at as high as 10.50% or 50% fishmeal replacement sustained environmental impacts associated with solid wastes compared to LMW-free diets (P > 0.05). Overall, this study underscores the suitability of LMW as a protein source in the diet for European perch, positively affecting growth performance, health status, sensory attributes of fillets, and environmental impact indicators. Nonetheless, careful attention should be given to the nutritional profile, particularly essential fatty acids in fish fillets.