Hematology and agglutination titer after polyvalent immunization and subsequent challenge with Aeromonas hydrophila in Nile tilapia (Oreochromis niloticus)

Abstract

This study evaluated the effects of polyvalent vaccination on the hematological and serum agglutination responses in Nile tilapia challenged with Aeromonas hydrophila. Two dosis, 1 x 104 and 1 x 108) Colony Forming Units (CFU)/mL, of vaccine containing the same amount of Aeromonas hydrophila, Pseudomonas aeruginosa and Enterococcus durans formalin-inactivated were tested by intraperitoneal (i.p) injection. Fish were challenged ten days after vaccination i.p. with a DL50-96h of 1 x 107 CFU A. hydrophila/mL. Samples were collected 48 h after challenging fish to check the hematological parameters, antimicrobial activity and agglutination titer of serum, samples were collected 48 h after challenge. Before challenge, the number of erythrocytes was higher in fish vaccinated with 1 x 108 CFU/mL. After challenge, total number of thrombocytes was higher in fish that received the greatest dose of vaccine. Before and after challenge, total number of leukocytes and the number of lymphocytes showed the highest values in vaccinated fish. Before challenge, increased number of monocytes in vaccinated and saline-injected fish was observed. The highest agglutination titer against A. hydrophila, P. aeruginosa and E. durans was related in 1 x 108 CFU/mL vaccinated fish. Before challenge, high values of antimicrobial activity in non-vaccinated fish and 1 x 108 CFU/mL vaccinated ones was also related. Therefore, after challenge, non-vaccinated fish and saline-injected ones showed the highest antimicrobial activity. This study showed that 10 days after immunization with a polyvalent vaccine at a concentration 1 x 108 CFU/mL, there was an increase on erythrocytes, leukocytes, thrombocytes and circulating lymphocytes production, while the glucose levels were reduced.