| Summary: | 碩士 === 國立屏東科技大學 === 水產養殖系所 === 105 === The aim of this study was to examine the effectiveness of microalgae and seaweed extracts in improving stress tolerances and disease resistance against pathogenic infection of the white shrimp Litopenaeus vannamei postlarvae. Firstly, fresh microalgae Chaetoceros gracilis (C. gracilis) and brown seaweed Sargassum crassifolium (S. crassifolium) were extracted with hot-water for 5 h. The fresh C. gracilis, C. gracilis extract, S. crassifolium extract were then analyzed for antioxidant activities. For the feeding trial, shrimp were fed four exprimental diets including (1) control (Artemia only); (2) Artemia enriched by fresh C. gracilis; (3) Artemia enriched with C. gracilis extract and (4) Artemia enriched with S. crassifolium extract. After 10 days of feeding, to evaluate the stress tolerances, shrimp were exposed to formaline at concentrations of 100, 150, and 200 ppm; or to ammonia at
concentrations of 40, 50, 60 mg L-1. In addition, to assess the disease resistance, shrimp were immersed in the seawater containing the pathogenic bacteria Vibrio parahaemolyticus at the dose of 1×105 CFU mL-1. Mortalities of shrimp were recorded. The results showed that polysaccharide content in C. gracillis extract was significantly higher than that of S. crassifolium extract (p<0.05). Total polyphenolic compounds in C. gracillis extract was significantly lower than that of fresh C. gracillis and S. crassifolium extracts (p<0.05). The highest flavonoid content was found in S. crassifolium extract. S. crassifolium extract showed the highest antioxidant activities as DPPH scavenging, ferrous ion chelating, and superoxide anion scavenging activities with values of 52.5±1.38%, 8.69±0.86%, and 24.8±2.48%, respectively. S. crassifolium extract treatment showed the best shrimp survival rate of 99.3±0.83%. However, the shrimp survival rate was only 83.8±1.06% in Control treatment. The shrimp survival rate of fresh C. gracilis and C. gracilis extract treatments were 90.8±1.22% and 96.5±0.61%, respectively. Shrimp fed with S. crassifolium extract also had significantly higher stress tolerances and disease resistance than those fed with fresh C. gracillis and C. gracillis extract. Therefore, it is concluded that S. crassifolium extract could be used as a potential additive to reduce the mortality of white shrimp at the postlarvae stage.
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