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.

盐度是重要的环境因素，通常在虾类养殖系统中没有注意到。在本研究中，人们尝试分析斑节对虾对急性盐度胁迫下哈维弧菌感染的生理和免疫反应。通过肌肉注射在5‰盐度，35‰盐度和最佳盐度（15‰）条件下用哈氏弧菌挑战虾。维持对照而无细菌攻击。血淋巴从虾收集后不久之前，盐度变化哈维氏弧菌的挑战（后盐度变化天（PSD）0），在攻击后一天（PCD）2,7和10免疫变量即总血细胞计数（THC），苯酚氧化酶活性（PO），硝基蓝四唑盐（NBT）还原，碱性磷酸酶活性（ALP），酸性磷酸酶活性（ACP）和代谢变量，即总蛋白（TP），总然后测定碳水化合物（TC），总游离氨基酸（TFAA），总脂质（TL），葡萄糖（G1）和胆固醇（Ch）。一种方法是ANOVA，然后是Duncan对方法的多次比较，结果表明，在不同盐度条件下，然后用哈氏弧菌攻击的虾之间存在显着差异（P < 0.05）。维持在15‰的虾挑战后存活率显着更高，而急性盐胁迫降低了存活率。但是，致病性哈维氏弧菌在35‰处比在5‰处略高。在盐胁迫，参数的发作即。，THC，NBT和ACP显著减少，并且在TC 5‰和35‰增加。继哈维氏弧菌的挑战，总体增加可能在PCD2上PCD2代谢参数和免疫变量进行观察和7斑节对虾与对照相比保持在15‰。即使在盐度胁迫下与对照相比，在盐胁迫下虾的免疫应答和代谢变量增加，但与维持在15‰的虾相比，其含量还是相当低的。回归分析证明，NBT，ALP，TP和TL可以作为潜在的压力指标来评估虾的健康状况。简而言之，从研究中可以得出结论，盐度的急性变化会引起生理反应，从而影响斑节对虾对哈维弧菌攻击的免疫能力和代谢性能，从而增加对感染的敏感性。此外，较高的盐度增强了哈维弧菌的致病性。