Solid-state Volvariella volvacea-fermented rice milling by-product as a potential sustainable alternative protein source to soybean meal in juvenile milkfish (Chanos chanos) diet

The present study evaluated solid-state Volvariella volvacea- fermented rice bran (VFRB) as a potentially sustainable alternative protein source to soybean meal (SBM) in diets for juvenile milkfish ( Chanos chanos ). A 60-day feeding trial was conducted following a completely randomized design with five dietary treatments in triplicate: a full SBM-based control and diets in which SBM was replaced with VFRB, at 25, 50, 75, and 100% by weight. Experimental diets were crude protein, lipid, and energy levels of 37%, 11%, and 4,475–4624.47 kcal/kg, respectively. Results showed that complete replacement (100%) of SBM with VFRB did not result in statistically detectable reductions in survival, growth performance, feed utilization, nutrient retention, whole-body composition, intestinal morphology, and gut microbial counts. Notably, the 50% VFRB diet significantly improved weight gain, specific growth rate, protein and lipid retention, and protein efficiency ratio while reducing the feed conversion ratio compared with the control. Furthermore, fish fed the 50% VFRB diet exhibited improved intestinal villi absorptive morphology, lower total gut bacterial counts, and higher gut lactic acid bacterial counts. These findings demonstrate that complete replacement of SBM with VFRB did not result in statistically detectable reductions in measured physiological response performance, while 50% replacement enhances responses including growth, nutrient utilization, and improved intestinal morphology. Overall, VFRB represents a potentially sustainable, functional alternative protein source that can reduce reliance on conventional soybean meal in juvenile milkfish aquaculture feeds.