Nutrient retention and feed utilization efficiency in <i>Clarias gariepinus</i>: The role of lysine and methionine in enhancing protein deposition and reducing nitrogen waste

The increasing shift towards plant-based protein sources in aquafeeds has necessitated optimizing nutrient retention and feed utilization efficiency to ensure sustainable aquaculture practices. This study evaluated the effects of lysine and methionine supplementation on protein deposition, feed efficiency, and nitrogen waste reduction in Clarias gariepinus. A completely randomized design (CRD) was used to assign 525 juvenile fish to six dietary treatments containing graded levels of lysine and methionine, with each treatment replicated three times. Fish were fed at 5% of their body weight thrice daily for eight weeks, after which growth performance, nutrient retention efficiency, and nitrogen waste excretion were analyzed. The results revealed that fish fed the highest lysine and methionine supplementation (1.00 g/kg each) exhibited significantly higher (P < 0.05) final weight (11.58 g), weight gain (5.27 g), and specific growth rate (0.29%/day) compared to the unsupplemented control (GL0: final weight = 4.67 g, weight gain = 1.27 g, SGR = 0.17%/day). Feed utilization was significantly enhanced, as indicated by an improved feed conversion ratio (FCR: 4.02) and protein efficiency ratio (PER: 0.74) in supplemented groups compared to the control (FCR: 7.28, PER: 0.54). Additionally, nitrogen retention efficiency (NRE) improved from 45.2% in GL0 to 74.5% in GL4, while total ammonia nitrogen (TAN) concentration decreased from 4.5 mg/L to 1.9 mg/L, reflecting better nitrogen metabolism and reduced environmental nitrogen loading. These findings demonstrate that lysine and methionine supplementation in plant-based diets significantly enhances nutrient retention, protein deposition, and feed efficiency while mitigating nitrogen waste accumulation. This study underscores the potential of amino acid supplementation in formulating sustainable, cost-effective, and environmentally friendly aquafeeds. Future research should explore long-term impacts on fish health, immune function, and environmental nitrogen dynamics in intensive aquaculture systems.