Department of Marine Biology, Microbiology and Biochemistry, School of Marine Sciences, Cochin University of Science and Technology, Fine Arts Avenue, Kochi, 682016, Kerala, India; Department of Zoology, Christian College Chengannur, Univeristy of Kerala, Chengannur, 689122, India.
Department of Marine Biology, Microbiology and Biochemistry, School of Marine Sciences, Cochin University of Science and Technology, Fine Arts Avenue, Kochi, 682016, Kerala, India.
Fish Shellfish Immunol. 2020 Nov;106:555-562. doi: 10.1016/j.fsi.2020.07.067. Epub 2020 Aug 6.
Salinity is an important environmental factor which usually goes unnoticed in shrimp growout systems. In the present study an attempt was done to analyse the physiological and immunological responses of Penaeus monodon to Vibrio harveyi infection under acute salinity stress. Shrimps were challenged with V. harveyi under 5‰ salinity stress, 35‰ salinity stress and optimal salinity (15‰) conditions by intramuscular injection. A control was maintained without bacterial challenge. Haemolymph was collected from shrimps soon after salinity change before V. harveyi challenge (post salinity change day (PSD) 0), on post challenge day (PCD) 2, 7 and 10. Immune variables viz., total haemocyte count (THC), phenol oxidase activity (PO), Nitroblue tetrazolium salt (NBT) reduction, alkaline phosphatase activity (ALP), acid phosphatase activity (ACP) and metabolic variables viz., total protein (TP), total carbohydrates (TC), total free amino acids (TFAA), total lipids (TL), glucose (Gl) and cholesterol (Ch) were then determined. One way ANOVA followed by Duncan's multiple comparison of the means revealed significant differences between shrimps subjected to different salinity conditions and then challenged with V. harveyi (P < 0.05). Post challenge survival was significantly higher in shrimps maintained at 15‰ and acute salinity stress reduced the survival rate. However, pathogenicity of V. harveyi was slightly higher at 35‰ than at 5‰. At the onset of salinity stress, parameters viz., THC, NBT and ACP significantly reduced and TC increased at 5‰ and 35‰. Following V. harveyi challenge, an overall increase could be observed in metabolic variables on PCD2 and immune variables on PCD2 and 7 in P. monodon maintained at 15‰ compared to the control. Even though an increase in immune response and metabolic variables could be obtained on post challenge days in shrimps under salinity stress compared to the control, it was considerably low in comparison with shrimps maintained at 15‰. Regression analysis proved that NBT, ALP, TP and TL could be proposed as potential stress indicators to evaluate shrimp health status. In brief, it may be concluded from the study that acute salinity changes evoke physiological responses that affect the immunocompetence and metabolic performance of P. monodon against V. harveyi challenge, thereby increasing the susceptibility to infection. Moreover higher salinity enhanced the pathogenicity of V. harveyi.
盐度是虾养殖系统中一个容易被忽视的重要环境因素。本研究试图分析在急性盐度胁迫下，斑节对虾对哈维弧菌感染的生理和免疫反应。通过肌肉注射，在 5‰盐度胁迫、35‰盐度胁迫和最佳盐度（15‰）条件下，对虾进行哈维弧菌挑战。对照组不进行细菌挑战。在进行盐度变化之前（盐度变化后第 0 天（PSD）0）、盐度变化后第 2、7 和 10 天（PCD），从虾中采集血淋巴。测定免疫变量，如总血细胞计数（THC）、酚氧化酶活性（PO）、硝基四唑盐（NBT）还原、碱性磷酸酶活性（ALP）、酸性磷酸酶活性（ACP）和代谢变量，如总蛋白（TP）、总碳水化合物（TC）、总游离氨基酸（TFAA）、总脂（TL）、葡萄糖（Gl）和胆固醇（Ch）。单因素方差分析（ANOVA）后，采用邓肯氏多重比较法对不同盐度条件下的虾进行比较，结果表明，与对照组相比，哈维弧菌感染的虾有显著差异（P < 0.05）。在 15‰和急性盐度胁迫下，虾的存活率显著提高，而急性盐度胁迫降低了存活率。然而，哈维弧菌在 35‰时的致病性略高于 5‰。在盐度胁迫开始时，参数 THC、NBT 和 ACP 显著降低，TC 在 5‰和 35‰时增加。在 15‰条件下，与对照组相比，哈维弧菌感染后第 2 天和第 7 天，代谢变量和免疫变量均有总体增加。与对照组相比，在盐度胁迫下的虾，尽管在感染后第 2 天和第 7 天的免疫和代谢变量有所增加，但与在 15‰条件下的虾相比，这些增加的幅度相当小。回归分析证明，NBT、ALP、TP 和 TL 可作为潜在的应激指标，用于评估虾的健康状况。简而言之，从本研究可以得出结论，急性盐度变化会引起生理反应，从而影响斑节对虾对哈维弧菌感染的免疫能力和代谢性能，从而增加其易感性。此外，较高的盐度会增强哈维弧菌的致病性。
