Effect of the hyperosmotic infiltration method on immune response in tilapia vaccinated with Streptococcus agalactiae

Abstract

This study aimed to evaluate the immune response in tilapia (Oreochromis niloticus) in optimum salinity for a vaccination with hyperosmotic infiltration in controlling streptococcosis caused by Streptococcus agalactiae. A total of 100 fish weighing 4.26 ± 1.37 g were immersed in water with a salinity of 0, 10, 20, and 30 g L−1 for 5 min, and then immersed in 109 cfu L−1 S. agalactiae vaccine for 30 min. The challenge test was carried out on 31 days post-vaccination with pathogenic S. agalactiae. Relative percent survival, blood profile, antibody titer, lysozyme activity, and fish blood glucose were measured on day 0, 15, and 30 post-vaccination and 10 post-challenge tests. The results showed that hyperosmotic infiltration with 20 g L−1 resulted in a higher relative percent survival of 88.24% compared to other treatments. Immunological parameters such as total erythrocytes, total leukocytes, hemoglobin levels, hematocrit levels, phagocytic activity, lysozyme as the non-specific immune system, and antibody levels as a specific immune system in fish immersed at 20 g L−1 before vaccination were higher than others. In conclusion, fish immersed in 20 g L−1 before immersion vaccination enhanced non-specific and specific immune defense and increased fish protection against pathogenic S. agalactiae.