Saekil Yun^a, Sib Sankar Giri^a, Hyoun Joong Kim^a, Sang Geun Kim^a, Sang Wha Kim^a, Jung Woo Kang^a, Se Jin Han^a, Jun Kwon^a, Woo Taek Oh^a, Cheng Chi^c, Jin Woo Jun^b, Se Chang Park^a,*

^a boratory of Aquatic Biomedicine, College of Veterinary Medicine and Research Institute for Veterinary Science, Seoul National University, Seoul, 08826, Republic of Korea
^b Department of Aquaculture, Korea National College of Agriculture and Fisheries, Jeonju, 54874, Republic of Korea
^c Laboratory of Aquatic Nutrition and Ecology, College of Animal Science and Technology, Nanjing Agricultural University, Nanjing, 210095, China

^*Corresponding author : Se Chang Park

Abstract
Immunization by bath immersion is likely the simplest method of fish vaccination. Although the route of immunogenicity has not been fully identified, immersion vaccination is clearly a useful labor-saving technique. In this study, microbubble (MB) treatment was assessed for its ability to improve the efficacy of bath immersion vaccination in the cyprinid loach. MBs are commonly defined as minute particles of gas with a diameter of less than 100 μm, which generated free radicals. Here, the efficacy of MB treatment for vaccination enhancement in the cyprinid loach was assessed in direct challenge experiments using the virulent Aeromonas hydrophila JUNAH strain; assessments comprised agglutination titer assay and non-specific parameter analysis. Agglutination titers were high in loaches that were immunized via injection with inactivated cells (FKC group); however, non-specific immune activation parameters (e.g., lysozyme, superoxide dismutase, and phagocytic activity) were more increased in loaches that were immunized via bath immersion with MB treatment. Moreover, MB-treated loaches showed comparable survival rates, relative to loaches immunized via injection with formalin inactivated cells. Thus, higher levels of non-specific immune parameters suggest increased efficacy of this vaccine approach. Improving the effectiveness of bath immersion vaccine will increase its affordability and ease of application in aquaculture.

Keywords : Bath immersion; Vaccine; Microbubbles; Formalin-inactivated cells; Aeromonas hydrophila; Cyprinid loach