Development of Immersion and Oral Bivalent Nanovaccines for Streptococcosis and Columnaris Disease Prevention in Fry and Fingerling Asian Seabass () Nursery Farms.

In the present study, chitosan-based bivalent nanovaccines of and were administered by immersion vaccination at 30 and 40 days after hatching (DAH), and the third vaccination was orally administered by feeding at 50 DAH. ELISA revealed that the levels of total IgM and specific IgM to and were significantly elevated in all vaccinated groups at 10, 20, and 30 days after vaccination (DAV). A qRT-PCR analysis of immune-related genes revealed significantly higher expression in the vaccinated groups compared to the control group, as revealed by 44-100-fold changes in the vaccinated groups compared to the control ( < 0.001) at every tested time point after vaccination. All vaccinated groups expressed , , and at significantly higher levels than the control group at 10 and/or 20 DAV ( < 0.05). In the challenge tests, the survival of vaccinated groups ranged from 62.15 ± 2.11 to 75.70 ± 3.36%, which significantly differed from that of the control group (44.44 ± 1.92%). Similarly, all vaccinated groups showed higher survival rates of 68.89 ± 3.85 to 77.78 ± 5.09% during challenge than the control groups (50.00 ± 3.33%) ( < 0.05).