Protease feed additives have been proven to improve digestibility and obtain improved growth while using less protein in aquatic feeds. Some of these protease complexes have been shown to have immunostimulant effects that significantly improve growth performance , survivability, and disease resistance in many commercially important aquaculture species . However, with the variety of available immunostimulants, differing feed preparation methods, and diversity of finfish and invertebrate species grown commercially, there is still the potential to optimize which concentrations of proteases would yield the most efficient, biologically beneficial, and cost- effective growth. One of the most economically important and versatile aquaculture species is the Whiteleg s hrimp Litopenaeus vannamei , known to tolerate salinities between 0.5 and 4 0 ‰.
To evaluate growth, phy siological, and immunological parameters of L. vannamei fed a diet containing differing amounts of a protease complex under low-salinity culture conditions, 360 shrimp ( mean ± SD = 0.35 ± 0.03 g ) were stocked equally into a low-salinity recirculating system consisting of 24, 67- L tanks. Four treatment diets were formulated, each containing 35% protein, 8% lipid , and 27% carbohydrates. Three of the four treatment diets contained 131, 175, and 208 mg/kg of Jefo’s AG-175 protease complex . Each treatment diet was fed to shrimp in six replicate tanks , four times daily, for six weeks. Final biomass, final individual weights , feed conversion ratios (FCR) , and weight gains were compared. Physiol ogical parameters including hemolymph osmolality, hemolymph ion concentrations, whole body proximate analysis, and intestinal histology were evaluated . Immunological parameters such as hepatopancreas gene expression and intestinal microbiota were analyzed. There were no differences in final individual weight (P = 0.0975) or weight gain (P = 0.2849) between treatments. There were differences in FCR (figure 1) between treatments . P hysiological and immunological results will be presented. The findings of this comprehensive study will determine which concentration of the AG-175 protease will yield the
most effective growth in low-salinity L. vannamei culture.