Development of novel protein feedstuffs is critical to support sustainable expansion of world aquaculture. Sorghum protein concentrate (SorgPC) is one such ingredient that is being produced at pilot scale and evaluated with several fish species. A digestibility evaluation and comparative feeding trial were conducted to assess the nutritional value of the SorgPC for Nile tilapia (Oreochromis niloticus). The SorgPC contained 50.1% crude protein with digestibility coefficients for organic matter, crude protein, lipid and gross energy determined to be 73.5%, 72.1%,63.3% and 70.0%, respectively. Availability values for all amino acids ranged between 70-99%. Subsequently, a Reference diet was formulated to contain 34% crude protein primarily from dehulled, solvent-extracted soybean meal (48.2% of diet), soy protein concentrate (7.6% of diet), and Special Select menhaden fishmeal (2.9% of diet). Two series of test diets, either with or without fishmeal (FM), were prepared by including incremental levels of the SorgPC to replace incremental amounts of soybean meal (SBM) and soy protein concentrate (SPC) on an equal-protein basis. Tilapia fingerlings (4.45±0.10 g; average initial weight ± SD) were evenly distributed into 24, 38-L aquaria operated as a recirculating system and three replicates were fed each diet twice daily to apparent satiation throughout a 7-week trial.
All the diets were well accepted by the juvenile Nile tilapia and no physical abnormalities were observed in all treatments during the feeding trial. Fish fed the experimental diets increased by over 500% of initial weight with no significant (P>0.05) differences due to diet. In addition, feed efficiency, body condition indices, or whole-body proximate composition of fish fed the various diets were similar to those fed the Reference diet (Table 1).
Based on data from this study, SorgPC is a promising and acceptable alternative feedstuff for Nile tilapia, particularly when used to partially replace expensive ingredients like SPC and FM.