FEED-BASED VACCINE: A PRACTICAL AND EFFECTIVE APPROACH AGAINST STREPTOCOCCOSIS IN CAGE-CULTURED RED TILAPIA IN MALAYSIA  

Streptococcosis in red tilapia is caused primarily by Streptococcos agalactiae and persists as a major disease problem in red tilapia both in Malaysia and other countries. Reported outbreaks have been reported as early as 2000 until now, causing high mortality resulting in high economic losses. Feed-based vaccine was thus developed to prevent Streptococcosis providing a more practical and easy measure for application. Therefore a field study was conducted in Kenyir Lake, Terengganu to evaluate the field efficacy of adjuvant inactivated vaccine (formalin-killed) incorporated in feed and administered orally following precise feeding regime. Three groups consisting of single booster, double booster and control group each was stocked with 1000 fishes/cage in duplicates at a selected endemic private farm during the critical period. Tilapia was vaccinated at 100 ± 20 g under field condition and sampling were done bimonthly for a period of 4 months. Samples were examined for prevalence rate of S.agalactiae including their antibody (IgM) titer. The mean prevalence rate for each group throughout study was recorded at 3.3%, 2.5% and 12.5%, respectively. At the end of study, survival of experimental group, double booster, single booster and control group was recorded at 75.1%, 65.3% and 47.2% respectively. High antibody titer recorded from double booster vaccination regime throughout the study showed that tilapia was protected against streptococcal infection. Thus oral vaccine could be a potential way of administration as it is easy and much more economical.