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Immersion vaccination is dependent on the response of fish mucosa-associated tissues. Herein, javelin goby Synechogobius hasta was immersed with Vibrio vulnificus bacterin to investigate mucosal and humoral immune responses post-vaccination. The results showed that the specific serum antibody titers gradually increased after vaccination and peaked at day 21, while the mucosal antibody titers in the gill, skin, and intestine showed a faster response, with the peak time at days 3, 5, and 7, respectively. For antigen uptake, a rapid and significant enhancement was detected in the mucosa-associated tissues (gill, skin, and intestine) compared with the blood, spleen, kidney, and liver (P < 0.05). Antigen uptake levels in the gills and skin were peaked at 12 h post-immersion and were significantly higher than other tissues (P < 0.05). The histological results showed that the mucous cell numbers in mucosa-associated tissues increased over time, peaked at day 3 post-immunization, and then decreased to the level of the control groups. Additionally, the mucin components in mucosa-associated tissues shifted from neutral mucopolysaccharide to acidic mucopolysaccharide. Integrations of antibody titers, antigen uptake in mucosa-associated tissues, mucous cell number changes, and mucin characteristic changes provided valuable information for research on mucosal immunity in fish. All present findings suggest a major advantage of immersion vaccines to elicit a high level of local immune response, making immersion vaccines an ideal mode of inoculation that induces protective immunity against a variety of pathogens. [ABSTRACT FROM AUTHOR]

Black rockfish (Sebastes schlegelii) is a marine fish with high financial value; however, the frequent occurrence of bacterial diseases has caused a production decline and economic losses. This study found that hyperemia, hemorrhage, and ascites were common in S. schlegelii during the V. parahaemolyticus infection. Inflammation, degeneration, and necrosis in the liver could be observed. The epithelial mucosal integrity, the intestine epidermis thickness, the villus heights, and the number of mucous cells in the intestine were decreased after infection. Apparent differences in most of the hematological parameters between the two groups were observed, such as the corpuscular volume (CV) and NaCl concentrations of the beginning hemolysis were decreased remarkably (P < 0.01) after infecting with V. parahaemolyticus. However, the white blood cell count (WBC), lysozyme (LZM), malondialdehyde (MDA), K+, Cl−, and Ca2+ were increased significantly (P < 0.01) after infection. In addition, the mRNA expressions in four tissues (gills, liver, blood, spleen) of eleven immune-related genes were investigated. The results showed that C1r, C1s, and C1inh expression varied considerably among tissues. Caspase 10 expression was reduced in four tissues after infection, but MyD88, TNF receptor, TNF-α, BAFF, IL-1β, IL-8, and IL-10 showed increased expression profiles within 24 h after infection. In particular, IL-1β expression in the liver and spleen increased 123.67 and 104.94-fold at 6 hpi, respectively. Therefore, in addition to pathology, the hematological detection and gene expression profiles could be used in the evaluation of healthy status in fish, and this study provided a preliminary basis for the diagnosis of S. schlegelii infecting with V. parahaemolyticus. [ABSTRACT FROM AUTHOR]