Partial replacement of fish meal with biologically fermented fish silage meal enhances nutrient utilisation in striped catfish (Pangasianodon hypophthalmus)

Fish-processing residues represent a promising resource for circular aquafeed production, with the potential to reduce dependence on conventional fish meal while improving nutrient-use efficiency. This study evaluated the effects of replacing the fish-meal fraction of diets for juvenile striped catfish ( Pangasianodon hypophthalmus ) with biologically fermented fish silage meal (FSM). Five diets were formulated to provide 0, 25, 50, 75, or 100% replacement of the fish-meal fraction and were tested in a completely randomised design. Fish were fed to apparent satiation three times daily. Apparent digestibility, nutrient retention, growth performance, digestive-enzyme activity, haematological and serum biochemical indices, water quality, ammonia excretion, and nitrogen- and phosphorus-related waste indicators were assessed. The FSM50 diet produced the highest apparent protein digestibility (97.57%), energy digestibility (81.65%), and protein retention (34.09%). It also yielded the lowest numerical feed-conversion ratio (1.13), while survival remained 100% in all treatments. Ammonia excretion was numerically lowest in FSM50 (0.012 mg TAN g-1 h-1). By contrast, complete replacement was associated with lower digestive-enzyme activities and higher total ammonia nitrogen, nitrite, and total suspended solids than the intermediate replacement treatments. Overall, replacing approximately half of the fish-meal fraction with biologically fermented FSM maintained growth and survival while improving selected indicators of nutrient utilisation. Further work using strictly isoenergetic and isonitrogenous diets, independent water circuits, and complete nutrient mass balances is required to confirm the environmental and production-scale benefits.