Efficacy of formalin-killed Streptococcus agalactiae vaccine in Nile tilapia (Oreochromis niloticus L.)

Abstract

The formalin-killed Streptococcus agalactiae vaccine in Nile tilapia (Oreochromis niloticus L.) was evaluated in terms of its efficacy at different immersion time. The highest and lowest survival rate was recorded in T1 (93.33±4.71%) and T2 (22.31±15.68%), respectively. Fish in T1 were not experimentally challenged with the pathogenic bacterium while fish in T2 were not vaccinated but challenged with the bacterium. The relative percent survival (RPS) of vaccinated groups (T4 = 53.06±25.71%, T5 = 49.42±37.57%, T3 = 36.57±29.18% and T6 = 36.32±6.71%) showed no significant difference to each other (p>0.05). Treatment 4 via 1-hour immersion attained the highest level of protection against the virulent S. agalactiae as compared to T3 (30 minutes’ immersion), T5 (90 minutes’ immersion) and T6 (120 minutes’ immersion). Fish in T2 to T6 already exhibited the same physical/clinical signs of bacterial infection such as corneal opacity, bleeding at the base of the fins, lethargy in swimming, erratic swimming, loss of appetite and/or difficulty in breathing.