Effects of substituting fish meal with poultry by-products and/or black soldier fly larvae on the growth performance, chemical composition, bioactivity, and hematological, microbial, histological, and immunohistochemical parameters of Nile tilapia

The demand for fishmeal is increasing, but its supply is stagnating or even declining. There is an urgent need to find an eco-friendly and cost-effective alternative protein source. This study evaluated poultry by-product and insect meal as alternatives to fishmeal for the health performance and bioactivity of Nile Tilapia. A Nile tilapia fry was divided into four groups with three replicates (No = 168). The first group was fed a basal diet containing 20% fishmeal (T_FM). The second, third, and fourth groups received a basal diet where the fishmeal was substituted with poultry by-product meal (T_PM), insect meal from Hermetia illucens (T_IM), and a mixture of poultry by-product and insect meal (T_MIX), respectively. The overall growth performance data indicated that T_IM achieved the best growth rates and feed utilization, comparable to T_FM (P > 0.05). T_IM, followed by T_PM and T_MIX, achieved a comparable high selling price while maintaining a lower total cost, resulting in better economic efficiency compared to T_FM. The T_IM diet also exhibited the highest total phenolic content, and both T_IM and T_FM showed superior antioxidant activity in the diets and the fish muscle. There were no abnormal hematological or serum biochemical parameters observed in Nile Tilapia fed insect meal and/or poultry by-product (all P-values > 0.05). The fish fillet samples from all groups were microbiologically safe for human consumption. Fish fed T_IM displayed the lowest levels of TNF-α and the highest levels of IL-10 (P < 0.05). All the groups exhibited normal architecture of the internal organs. The highest recorded absorption surface area (ASA) was found in both T_FM and T_IM diets. Immunostaining for NF-κB showed no significant changes among the experimental groups. Based on this study, we suggest that the insect meal can be a sustainable and cost-effective substitute for conventional fishmeal in aquaculture feed formulations.