Coated Crystalline Amino Acid Supplementation May Assist Higher Soybean Meal Inclusion in Diets for Nile Tilapia (Oreochromis Niloticus) With Improved Protein Assimilation and Retention

Abstract

The aquaculture industry has previously relied on high-quality fishmeal (FM) to fabricate diets of excellent standards. However, plant-based proteins such as soybean are more economic for low-value fish species, for example, tilapia and carp, and fishmeal use has been significantly lessened. Previous studies have addressed standard soybean meal (SBM) sources in aquafeeds seldom addressing essential amino acid correction. An eight-week feeding trial was conducted to evaluate the replacement of fish meal with soybean meal concentrate in Nile tilapia (Oreochromis niloticus) using a semi-purified diet against a Low Temperature (LT) fishmeal as a primary reference protein. Four diets with varying 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 supplementation with two essential amino acids: lysine and methionine (80SBPCAA) in a coated form. Daily growth values highlight similar rates when tilapia was fed 100FM and 40SBPC diets. No differences were observed in the final mean weights 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 80SBPCAA diet showed a significantly improved percent weight gain for tilapia compared to the 80SBPC-fed tilapia. PER 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 in juvenile tilapia. Crystalline coated essential amino acid supplementation showed marginal improvement of performance for tilapia at high SBPC inclusion level.