This study aims to evaluate the effects of immersion vaccination through hyperosmotic treatment, and determine the optimum hyperosmotic salinity for largemouth bass (Micropterus salmoides) by determining immune responses and protective efficacies post vaccination. For hyperosmotic immersion (HI), M. salmoides were immersed in three hyperosmotic salinities (5, 10 and 20‰ salinity) respectively, then transferred into normal freshwater containing inactivated Aeromonas veronii. For direct immersion (DI) group, fish were directly immersed in freshwater with the same concentration of bacterin. Non-specific immune responses were evaluated based on the analysis of nonspecific humoral substances and immune related genes (interleukin 1β, CD40, IL-8 and tumor necrosis factor α), the results showed that serum lysozyme and myeloperoxidase activities were appreciably up-regulated earlier and maintained higher levels in HI groups than DI group, highest activities were observed in 10‰ salinity HI group. The expression dynamics of immune related genes had similar trend with nonspecific humoral substances. For specific cellular immune responses, the percentages of surface membrane immunoglobulin-positive (sIg⁺) cells in DI group did not show any significant increase until at 14 day post immunization (dpi) and peaked at 35 dpi (23.17%), sIg⁺ cells in HI groups showed a marked rise 7 days earlier than DI group, then steadily increased and peaked at 28 dpi (5‰ salinity: 25.83%; 10‰ salinity: 32.03%; 20‰ salinity: 24.17%). The serum specific antibody level showed obvious increase in all vaccination groups since 7 dpi, it reached the peak at 28 dpi in HI groups (5‰ salinity: OD = 0.49; 10‰ salinity:OD = 0.71; 20‰ salinity:OD = 0.50), one week earlier than DI group. Both sIg⁺ cells and specific antibody level were highest in the 10‰ salinity HI group. The relative percent survival (RPS) was 68.42%, 89.42% and 63.16% in 5, 10 and 20‰ salinity HI groups, respectively, higher than this in DI group (47.37%). These results demonstrated that HI at 10‰ salinity could efficiently enhance the immune responses of M. salmoides and provide higher RPS. This has significant value for hyperosmotic immersion with bacterin in M. salmoides.

这项研究旨在评估高渗处理浸泡疫苗接种的效果，并通过确定疫苗接种后的免疫反应和保护功效来确定大嘴鲈（Micropterus salmoides）的最佳高渗盐度。对于高渗浸没（HI），将鲑鱼M. salmoides分别浸入三种高渗盐度（5、10和20‰盐度）中，然后转移到含有灭活的维罗纳气单胞菌的正常淡水中。对于直接浸泡（DI）组，将鱼直接浸泡在具有相同浓度细菌素的淡水中。根据对非特异性体液物质和免疫相关基因（白介素1β，CD40，IL-8和肿瘤坏死因子α），结果表明，血清溶菌酶和髓过氧化物酶活动是明显更早上调并保持在HI组比DI组更高的水平，在10‰盐度HI组中观察到最高活性。免疫相关基因的表达动力学趋势与非特异性体液物质相似。对于特定的细胞免疫反应，DI组中的表面膜免疫球蛋白阳性（sIg ⁺）细胞百分比直到免疫后14天（dpi）才显示任何显着增加，并在35 dpi（23.17％）时达到峰值，sIg ⁺HI组的细胞比DI组提前7天出现明显的上升，然后稳定增加并达到峰值（28 dpi）（5‰盐度：25.83％； 10‰盐度：32.03％； 20‰盐度：24.17％）。从7 dpi开始，所有疫苗接种组的血清特异性抗体水平均显着增加，在HI组中达到28 dpi的峰值（5‰盐度：OD = 0.49; 10‰盐度：OD = 0.71; 20‰盐度：OD = 0.50 ），比DI组提前一周。在10‰盐度HI组中，sIg ⁺细胞和特异性抗体水平最高。5、10和20‰盐度HI组的相对存活率（RPS）分别为68.42％，89.42％和63.16％，高于DI组（47.37％）。这些结果表明，盐度为10‰的HI可以有效增强沙门氏菌的免疫反应。并提供更高的RPS。这对于在沙门氏菌中用细菌浸入高渗具有重要的价值。