Coated crystalline essential amino acid supplementation supports high soybean meal inclusion in diets for Nile tilapia (Oreochromis niloticus) with improved protein retention and nutrient assimilation

Abstract The aquaculture industry has previously relied on high-quality fishmeal (FM) to produce diets of excellent standards. However, plant-based proteins such as soybean are more cost-effective for low-value fish species, for example, tilapia and carp, and fishmeal use has been significantly diminished. Previous studies have mainly addressed standard soybean meal (SBM) sources in aquafeeds. A 55-day feeding trial was conducted to investigate the replacement of fish meal with soybean meal concentrate in Nile tilapia ( Oreochromis niloticus) using a semi-purified diet approach against a Low Temperature (LT) fishmeal as a primary reference protein. Four diets with different levels of soybean meal were evaluated and compared to a control diet of 100 % fish meal. Three diets containing 20, 40, and 80 % soybean protein concentrate (SBPC) were examined. The fourth diet consisted of 80 % SBPC and two essential amino acids: lysine and methionine (80SBPC AA ) in a coated form. The average daily growth values highlight similar daily growth rates when tilapia was fed 100FM and 40SBPC. No significant differences were observed in the final mean weight for all soybean-fed tilapia, but they were marginally lower than the 100FM control diet group. The 80SBPC diet showed the poorest feed conversion ratio (FCR) at 1.31 and protein efficiency ratio (PER) at 2.19. However, the 80SBPC AA diet showed a significantly improved result for per cent weight gain compared to the 80SBPC-fed tilapia. Also, protein efficiency ratio was significantly higher at 2.47 and had a better Apparent Net Protein Utilization (ANPU) value of 28.51 % compared to un-supplemented 80SBPC-fed tilapia (25.48 %). These results confirmed that high-quality fishmeal can be substituted by up to 40 % SBPC alone and without any detrimental effects on growth or carcass composition. Further studies on plant proteins and supplementary amino acids as a suitable alternative for replacing high-quality fishmeal may promote a more sustainable aquaculture industry.