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

Abstract

In the present study chitosan-based bivalent nanovaccines of S. iniae and F. covae 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 S. iniae and F. covae 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 IgT expression in the vaccinated groups compared to the control group as revealed by 44�0-fold changes in the vaccinated groups compared to the control (p < 0.001) at every tested time point after vaccination. All vaccinated groups expressed IgM MHCII? and TCR? at significantly higher levels than the control group at 10 and/or 20 DAV (p < 0.05). In the S. iniae 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 F. covae challenge than the control groups (50.00 ? 3.33%) (p < 0.05). ? 2023 by the authors.