密度胁迫对凡纳滨对虾生长及非特异性免疫因子的影响

 【目的】分析由不同放养密度引起的密度胁迫对凡纳滨对虾（Litopenaeus vanname）生长和非特异性免疫因子的影响，以及主要水质因子的变化特点，探讨密度胁迫与水质因子对工厂化高密度养殖条件下对虾生长的作用机制。【方法】设置2个养殖系统，第一系统设置150、300、600和900尾/m3 4个养殖密度，形成密度胁迫梯度；第二系统采用较低养殖密度（30尾/m3），养殖用水来自对应的第一系统的排放废水，目的是分离水质因子与密度胁迫对对虾生长的影响。【结果】第一系统各处理凡纳滨对虾的体长增长、体重增长、存活率、SGRL和SGRW均受养殖密度的显著影响（P＜0.05），表现为各项指标随养殖密度的增加而降低。第二系统的存活率、体长增长、体重增长、酚氧化酶（PO）活力、过氧化物酶（POD）活力、抗菌活力（Ua）和溶菌活力（Ul）高于第一系统对应处理，而超氧化物歧化酶（SOD）活力低于第一系统，系统间水质因子的差异不显著。【结论】凡纳滨对虾（体长＜7.6 cm或体重＜6.1 g）养殖密度为150～900尾/m3时，造成对虾生长和非特异性免疫因子差异的主要原因是密度胁迫，水质因子的作用是次要的。

Effects of Intensity-Stress on the Growth and Non-specific Immunity Factors of Litopenaeus vannamei

Two culture systems were designed to classify the effects of intensity-stress and water quality factors on the growth of shrimp. In the first system, shrimps Litopenaeus vanname, were cultured at 150, 300, 600 and 900 individuals/m3. In the second system, shrimps were cultured　with water drained from the first system. The growth, survival and non-specific immunity factors (PO、SOD、POD、Ua and Ul) of shrimp cultured in each system were determined. The results showed that weight gain, length gain and survival rate reduced with the increase of stocking intensity in the first system. Survival rate, weight and length gain, the activities of PO、POD、Ua and Ul of shrimp in the second system were higher than those of shrimp cultured in the first system, but SOD activity of shrimp in the first system was higher than that of the second system. There are no significant differences in water quality factors (TAN、NO2-N、NO3-N and PO4-P et al.) between the two systems, which suggested that the primary reason for the difference of shrimp growth and enzyme activities in the two systems was intensity-stree, while water quality only played a minor role.