Introduction
Disease outbreaks and climate change have been an ongoing challenge for some large Asia shrimp aquaculture producers, particularly in Thailand and China. In Thailand, shrimp diseases are the most important causative agents. The currently pathogenic bacteria and viruses are Vibrio harveyi and V. alginolyticus as well as acute hepatopancreatic necrosis disease (AHPND) and early mortality syndrome (EMS) caused by V. parahaemolyticus (Lightner, 2011). Furthermore, stress is universal challenge in animal and it can be defined as the nonspecific response of the body to any demand made upon it. Stress can cause adverse effects in animals like low productivity, susceptibility to disease, organ damage, retarded growth and death. (Chen,2015). Dietary vitamin C is essential for penaeid shrimp, and its deficiency would induce severe damage, such as the “black death” syndrome. It also acts as a promising nutritional supplement, since it has been already demonstrated that this vitamin, besides functioning as a potent antioxidant such as an immunostimulant in fish and crustacean (Maggioni et al., 2004). Many herb extracts have the function related to vitamin C on animal physiology. Phytocee, herb extract, has the adaptogenic effect which could be understood by examining its ingredient. Withania somnifera, one of the key ingredients has been shown to have anti-stress effects and improve immunity in animals (Singh, 2011). There fore, the aim of this study was to evaluate the effects of ratio between vitamin C phosphate (vit-C phosphate) and Phytocee on growth performance and survival after pathogen challenge test.
Material and Methods
The experiment was a factorial design with 2 factors of A : 2 levels of vit- C phosphate 35% (0 and 1000 ppm) and B: 2 levels of Phytocee (1000 and 2000 ppm) with 4 treatments and five replication as Table 1.
Shrimp with initial mean weight of 1.4 g/shrimp were randomly distributed into 240L glass aquarium (Total 20 aquariums) that contained 120L of 15 ppt seawater and stocked 30 shrimp per aquarium (250 pcs/m3). During 8 weeks of feeding trial, shrimp were fed experimental diets 3-5%BW, 4 times a day and weighted on week 0, 4 and 8 for determined growth performance and after challenge test by bath treatment against 6.2X105 CFU/ml of Vibrio parahaemolyticus AHPND for 12 days, mortality was recorded.
Results
After 8 weeks of feeding trial, the growth performance of shrimp fed different ratio between vit-C phosphate and phytocee (herb extract) in diets showed that shrimp fed diets of vit-C phosphate 1000 ppm had better growth performance than group of shrimp fed vit-C phosphate 0 ppm (p<0.05). Moreover, shrimp fed diets of Phytocee 2000 ppm had better growth performance than shrimp fed Phytocee 1000 ppm (p<0.05). Hence, shrimp fed Phytocee 2000 ppm exhibited the better performance than group of shrimp fed diet of Phytocee 1000 ppm both with vit-C phosphate 0 and 1000 ppm (p<0.05) when focusing on final weight, average daily gain, and shrimp production (T4>T3,T2,>T1). Feed utilization in term of feed conversion ratio in shrimp fed Phytocee 2000 ppm was lower (p<0.05) than shrimp fed Phytocee 1000 ppm both in shrimp fed vit-C phosphate 0 and 1000 ppm (T4<T2<T3<T1). The results of growth performance and feed utilization were presented in Figure1. The survival rate were not significantly differences (p>0.05). Shrimp fed vit-C phosphate 0 ppm have tended to present the poor survival rate than shrimp fed vit-C phosphate 1000 ppm (p=0.063) both in shrimp fed Phytocee 1000 and 2000 ppm and Phytocee 2000 ppm demonstrated the better survival rate than 1000 ppm. The survival rate was 82.67, 85.33, 86.00 and 88.67% in T1, T2, T3 and T4, respectively. The levels of Phytocee did not affect the survival rate under high stocked density of 250 shrimp/m 3 in clear water of indoor condition due to proper culture management resulting exhibited on promote growth performance and shrimp production. After disease challenge by V. parahemplyticus AHPND immersion treatment, the survival rate of shrimp fed vit-C phosphate and Phytocee showed that shrimp fed vit-C phosphate 1000 ppm and phytocee 2000 ppm had highest survival rate follow by shrimp fed vit-C phosphate 1000 ppm and phytocee 1000 ppm (p<0.05) and the poor survival rate exhibited in shrimp fed vit-C 0 ppm (T4>T3>T2, T1). There, the results indicate the efficacy of vit-C and Phytocee on improving growth performance and survival rate under high stress condition of stocking density and disease challenge and imply that Phytocee has the adaptogenic effect on reducing stress resulting promoting growth performance and survival rate under stress condition.
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