pH水平和昼夜变化对池塘养殖凡纳滨对虾成活率的影响

为评价不同pH水平和昼夜变化幅度对凡纳滨对虾成活率的影响,采用单因素实验设计,实验Ⅰ设4个pH水平:6.6(P1)、7.6(P2)、8.6(P3)和9.6(P4),以温室养殖池塘内的平均pH水平(8.2)为对照(P0);实验Ⅱ设3个pH昼夜变化幅度:7.5～8.2(PV1)、7.5～9.5(PV2)和7.5～10.0(PV3),以养殖池塘的平均pH昼夜变化幅度(7.5～8.7)为对照(PV0)。结果显示,环境pH水平可显著影响对虾成活率、血淋巴颗粒细胞数以及血淋巴中超氧化物歧化酶(SOD)、谷胱甘肽过氧化物酶(GSH-Px)、谷胱甘肽还原酶(GR)、过氧化氢酶(CAT)、酚氧化酶(PO)和诱导型一氧化氮合酶(iNOS)的活性。P4水槽内对虾成活率显著低于P0、P1、P2和P3水槽,同时其血淋巴SOD、GSH-Px、GR、CAT、PO和iNOS的活性较后者不同程度地下降。pH昼夜变化幅度可显著影响对虾成活率、血淋巴SOD、GSH-Px、GR和CAT活性,但对血淋巴谷胱甘肽含量无显著影响。PV2和PV3水槽内对虾成活率显著低于PV0和PV1水槽,同时其血淋巴SOD、GSH-Px、GR和CAT活性较后者不同程度地降低。研究表明,环境pH水平及昼夜变化幅度可显著影响凡纳滨对虾的成活率。鉴于对虾死亡率变化伴随血淋巴SOD、GSH-Px、CAT和PO活性的变化,初步认为对虾死亡与pH胁迫产生的应激有关。因此,调控pH应是对虾池塘养殖水质管理中的一项重要措施。

Effect of pH variation on survival of Litopenaeus vannamei reared in ponds and its physiological mechanisms

Generally pH in the ponds of white shrimp Litopenaeus vannamei farming exhibits long term trend as well as diel variation. Understanding the effect of pH variation on survival of white shrimp is critical for improving water quality management in commercial white shrimp farming. In the present study, two independent experiments each with single factor design were conducted to evaluate the effects of pH level and magnitude of pH diel variation on survival of white shrimp. Meanwhile, the physiological mechanisms were analyzed. In experimental I, four pH levels (6.6, 7.6, 8.6 and 9.6) were evaluated, and the average pH level (8.2) observed in commercial ponds was used as control. In experimental II, three magnitude of pH diel variation (7.5 ~ 8.2, 7.5 ~ 9.5, 7.5 ~ 10.0) were evaluated, and the average magnitude of pH diel variation (7.5 ~ 8.7) observed in commercial ponds was used as control. The results showed that pH level can significantly affect survival of white shrimp, hemolymph cell count, and activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), glutathionereductase (GR), catalase (CAT), phenoloxidase (PO) and inducible nitric oxide synthase (iNOS) in vivo. Mortality of white shrimp significantly increased, while activities of SOD, GSH-Px, GR, CAT, PO and iNOS declined, when environmental pH climbed from 7.6 to 9.6. In the other hand, magnitude of diel pH variation can significantly affect survival of white shrimp and activities of antioxidant enzymes (SOD, GSH-Px, GR and CAT), but did not result in significant change in glutathione content. Mortality of white shrimp significantly increased, while activities of SOD, GSH-Px, GR and CAT decreased, when magnitude of diel pH variation was extended from 7.5 ~ 8.2 to 7.5 ~ 10.0. This study reveals that pH level and magnitude of diel pH variation are important environmental factors responsible to survival of white shrimp, and stress induced by unsuitable pH should be the physiology mechanisms since high mortality of white shrimp accompanied with the change in activities of SOD, GSH-Px, CAT and PO. According to the present study, it is recommended that proper pH control should be listed as an important content for environmental management in white shrimp pond farming.