Assessment of integration of black soldier fly larvae meal and yeast Yarrowia lipolytica in diets of Macrobrachium rosenbergii based on growth, nutrient digestibility, intestinal microbiota and phosphorus discharge

The growing demand for sustainable protein sources in aquaculture has driven interest in black soldier fly (BSF) larvae meal and yeast Yarrowia lipolytica (YL) as fishmeal alternatives. This study evaluated the effects of replacing fishmeal (0–80 %) with a 1:1 mixture of defatted BSF larvae meal and YL on growth, nutrient utilization, intestinal health, and phosphorus discharge in giant freshwater prawns (Macrobrachium rosenbergii). Five isonitrogenous experimental diets were formulated, with graded replacement levels of 0 % (control, BSF_YL0), 10 % (BSF_YL10), 20 % (BSF_YL20), 40 % (BSF_YL40), and 80 % (BSF_YL80). Juvenile prawns (initial weight: 0.25 ± 0.03 g) were fed the respective diets for 8 weeks. Key findings revealed that prawns fed 10–20 % replacement diets maintained comparable growth performance (P > 0.05), feed conversion ratios, and protein apparent digestibility coefficients to the fishmeal control. However, higher replacement levels (40–80 %) significantly compromised survival rates (P < 0.05), reduced immune-related enzyme activities (alkaline phosphatase, AKP; acid phosphatase ACP), and elevated oxidative stress markers (malondialdehyde, MDA). Notably, the 20 % replacement group demonstrated enhanced phosphorus retention efficiency and reduced phosphorus waste; improved digestive enzyme activities (trypsin and lipase); and beneficial modulation of intestinal microbiota, with significant enrichment of Bacteroidota, Actinobacteriota and Cloacibacterium. Transcriptomic analysis of hepatopancreas tissue identified 568 differentially expressed genes in the BSF_YL20 group, with significant enrichment in phagosome activity, protein digestion/absorption, and PI3K-Akt signaling pathways. While 20 % replacement showed environmental benefits, histological examination revealed mild hepatopancreatic damage and downregulation of digestive enzyme-related genes. In contrast, the 10 % replacement optimized intestinal villus morphology without compromising growth or immune function. These findings demonstrate that a 10 % fishmeal replacement with BSF-YL mixture is optimal for balancing growth and health in M. rosenbergii, while 20 % substitution may benefit environmental sustainability by reducing phosphorus discharge. The study provides critical insights into the synergistic use of insect and yeast proteins in aquafeeds, supporting eco-friendly aquaculture practices.