Effect of Dietary Protein Substitution of Fish Meal with Insect Larvae Meal on the Growth and Digestive Functions of Koi Carp Cyprinus carpio var. koi (Linnaeus, 1758) Fry in Nursery Phase

An 8-week feeding trial was conducted to evaluate the effects of two insect larvae meals such as silkworm pupae (Bombyx mori) meal and black soldier fly (Hermetia illucens) larvae meal as dietary protein substitutes for fish meal on the growth performance and digestive physiology of koi carp (Cyprinus carpio var. koi) fry. For that, 15 days old induced bred koi fry (2.28/ ±/ 0.24/ cm; 0.26/ ±/ 0.14/ g) were stocked in happas (10/ ×/ 3/ ×/ 1/ m) placed within an experimental earthen pond. Nine iso-nitrogenous (351.07/ g/ kg{¹) and iso-lipidic (71.98/ g/ kg{¹) experimental diets were formulated with insect meals replacing fish meal at 20%(SWP20,BSF20), 30%(SWP30,BSF30), 40%(SWP40,BSF40), and 50%(SWP50,BSF50) inclusion levels, alongside a control diet containing only fish meal. Results showed significantly higher (P/ </ 0.05) final length and weight gain in fry fed SWP50 (3.26/ ±/ 0.01/ cm; 3.79/ ±/ 0.01/ g) and BSF50 (3.22/ ±/ 0.01/ cm; 3.56/ ±/ 0.02/ g) diets. Growth indices including feed conversion ratio, feed efficiency ratio, protein efficiency ratio and survival rate were also notably improved in these groups. Furthermore, digestive enzyme activities were significantly elevated (P/ </ 0.05) in fry fed SWP50 and BSF50 diets, indicating enhanced nutrient utilization. These findings depicts that both the insect larvae meal can effectively replace 50% of fish meal with a dietary inclusion level of 147 g kg^-1 in the diet of koi carp fry without compromising growth, survival and digestive function.