| Litopenaeus vannamei is one of the most important shrimp varieties which has high production in the world. Because it owns the properties of high adaptability, rapid growth and disease resistance, it has been farmed widely in China since1988. In according to the report of Chinese fishery statistics yearbook in2011, the total production of shrimps was about2.38million tons in2010and the production of Litopenaeus vannamei was about1.23million tons which was more than50%of the total. In recent years, due to the effects of human activities and natural environment changes, the severity, incidence and duration of hypoxia are increasing. Moreover, with the enhancement of market demand and the progress of cultivation techniques, so the highly density and industrial aquaculture become the inevitable trend, which leads to the cultural ecosystem is very single fragile, and which increase the frequency of hypoxic occurrence in the aquatic water. Finally, hypoxia has adverse effects on the growth and development and farming of shrimp. So, investigating the rules of growth and development, hypoxia-resistant mechanism and breeding the hypoxia-resistant strains will be important to predict the growth rules, make scientific farming pattern and increase the culture benefits. This study focused on the growth and development rules, the main traits which affected body weight and the sensitive period of shrimp to hypoxia. Meanwhile, we also analyzed the changes of physiology and biochemistry and DNA damage levels caused by hypoxia and reoxygenation. These results will be benefit to farming, breeding and investigating the hypoxia-resistant mechanism of Litopenaeus vannamei. The main research results were as follows:1. The direct effect of body length on body weight was the largest, followed by total length, the third abdominal segment width and the first abdominal segment width, but they influenced indirectly body weight through body length. So body length was the optimal breeding select index.2. Gompertz was more suitable to simulate the growth curve of body weight. The fitting degree, inflection point of time and inflection point of body weight were0.855,169d and16.81g respectively. And Logistic model could better to simulate the growth curve of body length, and the fitting degree, inflection point of time and inflection point of body length are0.917,95d and74.44mm.3. The sensitivity to hypoxia was significantly different (p <0.05) at different life stages of Litopenaeus vannamei and the sensitivity of larva was higher than adult. Mysis Ⅲ was the most sensitive period in the whole life stages and its12h LC50was2.114ppm.4. Hypoxia could significantly reduce the total hemocyte counts (THC)(p <0.01) and it showed obvious time and dose effect. The THC of treatment group fell to the lowest level after reoxygenation for3h, and it did not return to normal level after reoxygenation for24h.5. Hypoxia could enhance hemocyanin concentration in the hemolymph of Litopenaeus vannamei, and induce the activities of alkaline phosphatase (AKP), acid phosphatase (ACP), superoxide dismutase (SOD) and glutathion peroxidase (GPX), and increase the concentrations of polphenol oxidase (PO) and malondialdehyde (MDA) in hepatopancreas, gill and hemolymph. But, PO concentration in hepatopancreas decreased at first then increased at1.5ppm, and then arrived at the highest level after reoxygenation for3h.6. Hypoxia could induce oxidative stress and DNA damage of hepatopancreas, gill and hemolymph. The results of DNA damage showed obvious time and dose effect and gradually returned to normal level during reoxygenation. |
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