We assessed swimming capacity, energy expenditure, and physiological responses of European perch (Perca fluviatilis) fed four isonitrogenous and isoenergetic diets containing yellow mealworm (Tenebrio molitor) larvae meal at 0, 25, 50, and 75% substitution for fishmeal (abbreviated diets, TM0, TM25, TM50, and TM75). Each diet was fed to quadruplicate group of perch (initial biometrics, body weight 20.81 ? 3.36 g, total length 11.77 ? 0.72 cm) for 119 days. At the terminal of feeding trial following 24 h starvation, eighty fish (20 fish/diet group) were individually selected for swimming performance tests, which were conducted in a 10 L enclosed swimming tunnel with velocity increased from 5 cm/s in 2 cm/s increments every 60 s. Exercised fish, fish experienced swimming tests, and non-exercised fish, fish not involved in swimming tests were, at the same time, sampled for serum biochemistry, muscle traits. Whole-body of non-exercised fish were also analyzed for proximate composition and fatty acid profile. Critical swimming speed (Ucrit, cm/s and body length/s), oxygen consumption (MO2, mg/kg/h), and energy cost of transport (COT, J/kg/m) of perch did not differ among diet treatments. Exercised perch significantly increased serum glucose and cortisol compared to non-exercised fish. Substitution of fishmeal by T. molitor larvae meal induced significant changes in aspartate aminotransferase across treatment groups, lactate dehydrogenase in TM0 and TM75, K+ concentration in fish fed TM75, and muscle water content in TM50 of exercised compared to non-exercised perch. Oleic acid of whole-body fish had a significant linear correlation with the critical swimming speed of European perch. Since fish swimming behavior is an indicator of animal welfare, our findings suggest that dietary insect meals could ensure the welfare of farmed fish.
