The efficacy of nile tilapia (Oreochromis niloticus) broodstock and larval immunization against Streptococcus agalactiae and aeromonas hydrophila

Abstract

Streptococcus agalactiae and Aeromonas hydrophila have been recognized as the causative agents of mortality in tilapia larvae with single infection and coinfection. The objective of this study was to evaluate the efficacy of maternal transfer and offspring protection from the immunization of monovalent and bivalent vaccines on Nile tilapia (Oreochromis niloticus) broodstock and larval immunization. Four groups of broodstock were intraperitoneally injected with formalin killed whole-cells of S. agalactiae (Sa group), A. hydrophila (Ah group), the bivalent mixed vaccine of them (Biv group), and phosphate-buffered saline as a control (Pbs group). Immunization of the larvae produced from immunized broodstock with a bivalent vaccine (Biv1 group) and Pbs (Pbs1 group) was performed by immersion at 20 days after hatch. Larvae produced from the Pbs group were unvaccinated as the control (Pbs2 group). Changes in the specific antibody and relative percent survival were measured. The Sa and Ah groups that could increase specific antibodies and protection against pathogenic bacteria were challenged with the homologous bacteria. The Biv group stimulated and protected against both S. agalactiae and A. hydrophila. The specific antibody of the Biv1 group was higher than the Pbs1 and Pbs2 groups. The last observation in this study showed that the relative percent survival of the Biv group after challenged S. agalactiae, A. hydrophila, and coinfection were 74.74 ± 3.18%, 73.81 ± 8.58%, and 71.48 ± 5.70%, respectively. The use of bivalent vaccines on the broodstock and larvae may be a strategy to reduce mortality in Nile tilapia larvae caused by single pathogen infection of S. agalactiae and A. hydrophila, or coinfection with both S. agalactiae and A. hydrophila.