| This thesis was divided into three stages: the first trial was that effects of different crowding stress on growth performance, water quality parameters of Penaeus vannamei. The second trial was that effects of different crowding stress on inmmune factors of Penaeus vannamei.The third trial, on the basis of previous studies, was conducted to evaluate the effectiveness of the high amount of dietary Vitamin C on improving the immune factors of Penaeus vannamei under the crowding stress. The results were summarized as follows:(1) Four stocking densities (200, 400, 600, 800ind/m3) were chosed to evaluate the effects of different crowding stress on growth performance and water quality parameters of Penaeus vannamei. Shrimps (initial body length: 1.5±0.1cm) were selected randomly to the glasses tanks (40cm×50cm×60cm) for 8 weeks. Sampling began at the seventh week. The result showed that the weight gain, survival rate and special weight growth rate(SGR), fat content, protein content were significantly affected by the crowding stress (p﹤0.05) and were decrease as the stocking density increased. The pH and ammonia-N were significantly affected by the crowding stress (p﹤0.05). And the pH was decrease with the stocking density increased; ammonia-N was increased as the different of stocking density.(2) Four stocking densities (200, 400, 600, 800ind/m3) were chosed to evaluate the effects of different crowding stress on immune factors of Penaeus vannamei. Shrimps (initial body weight: 3.0±0.5g) were selected randomly to 16 glasses tanks (40cm×50cm×60cm). Lysozyme (LYS), phenol oxide enzyme (PO), alkaline phosphatase (AKP) and superoxide anion (O2-) activities were conducted at the 1, 3, 5, 7, 10 day. The results should that immune factors including LYS, PO, AKP and superoxide anion activities took a low-high-low trend while the stocking density increased, especialy in high density groups (600, 800ind/m3). In the same density all of the immune factors were significiently effected by the crowding stress with the time increased (P<0.05). There was a significant positive correlation between the immune factors and the crowding stress (P<0.05) at the same time.(3) The study was conducted to evaluate the effectiveness of the high amount of dietary Vitamin C on improving the immune factors of Penaeus vannamei under the crowding stress. Experimental set up four stocking densities gradient (200, 400, 600, 800ind/m3). Shrimps (initial body length: 3.5±0.5m) were selected randomly to 16 glasses tanks (40cm×50cm×60cm). Lysozyme (LYS), phenol oxide enzyme (PO), alkaline phosphatase (AKP) and superoxide anion (O2-) activities were conducted at the 1, 5, 10 day. Feeding the dietary of Vitamin C was at the 11 day. Lysozyme (LYS), phenol oxide enzyme (PO), alkaline phosphatase (AKP) and superoxide anion (O2-) activities were at the 14, 18, 20 day. The results should that all of the immune factors were significiently improvement by the Vitamin C (P<0.05). The immune factors of Penaeus vannamei in the low density groups (200, 400 ind/m3) were significiently improved and were recovered to the pre-trial activity. The immune factors of Penaeus vannamei in the high density groups (600, 800 ind/m3) were improved but were significantly lower than the pre-trial activity of the immune system.
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