G lobal farmed crustacean pro- duction has been increasing at much faster rate than major farmed species. It is expected to reach 6.8 million metric tons (MMT) in 2015, of which, 69 percent or 4.7 MMT will be from the marine shrimps (Figures 1A, 1B). In the last 15 years, the production increased six-fold driven more by intensi- fication rather than expansion of the area cultivated. The development of specific pathogen free (SPF) broodstock of Pacific white shrimp has been the major contributing factor to this intensification, and the accompanied spectacu- lar growth. This has resulted in a much higher demand for compounded feed. The current demand for feed is estimated to be 6.8 MMT or 90 percent of the production. This is about four times higher than 1.75 MMT or 77 per- cent of the production in 2000 (Tacon and Metian, 2015). However, the over- intensification and improp- er management, the lack of proper knowledge on nutritional requirements at various stages and over or under formulation, and the increasing use of poorly digestible and poorly char- acterised protein sources while replacing fishmeal, usually cause unwanted stress and poor stress responses in the shrimps. As a result, occasional dis- ease outbreaks have been very common creating considerable economical losses in many countries. The addition of dietary protease is considered to be an important tool for better nutrient utilisation. It is hypoth- esised that a better nutrient profile and utilisa- tion can compensate poor immune or stress responses. Specially, when high quality ingre- dients are partially or completely replaced by more economical protein sources, which are often of poor quality. The study The study, consisting of five treatments, was conducted at the Guangdong Ocean University of China. The objective of the study was to assess the changes in immune response to low fishmeal diets supplemented with a commercially available dietary protease. Two diets were prepared: one with 20 percent fishmeal (positive control) and the other with 10 percent fishmeal (negative con- trol). The fishmeal was replaced by increas- ing peanut meal (16 percent) and soybean meal (28 percent) contents compared to 11 percent and 16 percent, respectively from the positive control diet for equal amount of crude protein. Another three diets were pre- pared by adding graded level (125, 150 and 175 ppm) of a commercial protease complex (Jefo Nutrition Inc., Canada) to the mash of the negative control diet. The activities of acid (ACP) and alkaline (AKP) phosphatases, superoxide dismutase (SOD) and polyphenol oxidase (PO) were analysed in both serum and hepatopan- creas of 15 shrimps per dietary treatment. The malon-di-aldehyde (MDA) content was analysed only in serum. Regression analysis was performed to assess the effects of the intake of dietary protease on these responses. No differences in enzymatic activities and MDA contents were observed between the shrimps fed the 20 percent fishmeal diets and the 10 percent fishmeal diets supplemented with 175 ppm protease. The results of the regression analysis with protease intake (µg/ shrimp) at 0, 125, 150, 175 ppm of the 10 by Hoongli Song, Guangdong Ocean University, Zhanjiang, China, Yao Liu, Nutritech Solutions Inc., Shanghai, China, Xiao-hui Dong, Guangdong Ocean University, Zhanjiang, China and M. A. Kabir Chowdhury, Jefo Nutrition Inc., Saint-Hyacinthe, Quebec, Canada Dietary protease improves immune responses in Pacific White Shrimp, Litopenaeus vannamei IMMUNE RESPONSE Table 1. Regression of the protease intake per shrimp with various immune parameters and 96-h cumulative mortality of shrimps fed graded level of protease Min Max Adj R2 MSE t-value Serum Acid phosphatase - ACP (KAU/ml) 2.6 5.9 72% 0.37 6.28*** Alkaline phosphatase - AKP (KAU/ml) 2.6 6.6 70% 0.55 5.9*** Superoxide dismutase - SOD (U/ml) 345.9 411.1 75% 73.43 6.8*** Phenol oxidase - PO (U/ml) 515.7 958.2 60% 8230.00 4.9*** Malon Di-Aldehyde - MDA (nmol/ml) 9.1 15.8 60% 2.40 -4.8*** Min Max Adj R2 MSE t-value Hepato-pancreas Acid phosphatase - ACP (KAU/ml) 55.9 132.9 46% 234.00 3.7*** Alkaline phosphatase - AKP (KAU/ml) 73.7 170.6 28% 556.00 2.6* Superoxide dismutase - SOD (U/ml) 4.1 7.3 75% 0.30 6.8*** Phenol oxidase - PO (U/ml) 657.4 1057.4 52% 8787.00 4.1*** Cumulative mortality (%) 25% 57% 61% 0.00 -4.9*** KAU - King-Armstrong Unit, amount of enzyme that will liberate 1 ml of phenol in 15 min; SOD U - inhibits the rate of increase in absorbance at 550 nm by 50%; PO U –the change in absorbance per min at 490 nm. For t-values: *** significant at 0.001; **significant at 0.01, *significant at 0.05. 32 | INTERNATIONAL AQUAFEED | May-June 2015 FEATURE