Evaluation of biofilm of Vibrio anguillarum for oral vaccination of Asian seabass, Lates calcarifer (BLOCH, 1790)

The present study evaluated the biofilm (BF) of Vibrio anguillarum for oral vaccination of Asian seabass, Lates calcarifer. An 80-day experiment was carried out in circular fiber-reinforced plastic (FRP) tanks using free cell (FC) and BF of Vibrio anguillarum with triplicate in each. Heat-inactivated FC and BF cells at 10⁷, 10¹⁰ and 10¹³ CFU/g fish/d were fed to fish for 20 days, agglutination antibody titer estimated at each 10 days interval up to 60-day post vaccination. As compared to FC and control there was a significant increase in agglutinating antibody titer in the biofilm vaccinated fishes. Among the 3 doses, BF at 10¹⁰ cfu/g fish/d was considered the ideal dose for vaccination. Relative percentage survival (RPS) was higher in biofilm vaccinated fish (85.4%) compared to that with free cells (27.0%). The study demonstrated the better performance of V. anguillarum biofilm oral vaccine compared that with free cell vaccine in L. calcarifer. The study further supports better performance of biofilm vaccine model with one more bacterial pathogen in a high carnivore fish.

Development and standardization of a monoclonal antibody-based rapid flow-through immunoassay for the detection of Aphanomyces invadans in the field

A monoclonal antibody-based flow-through immunoassay (FTA) was developed using a nitrocellulose membrane placed on the top of adsorbent pads enclosed in a plastic cassette with a test zone at the center. The FTA could be completed within 10 min. Clear purple dots against a white background indicated the presence of Aphanomyces (A.) invadans. The FTA limit of detection was 7 μg/mL for A. invadans compared to 56 μg/mL for the immunodot. FTA and polymerase chain reaction (PCR) could detect A. invadans in fish tissue homogenates at a 10(-11) dilution compared to a 10(-8) dilution by immunodot. In fish suffering from natural cases of epizootic ulcerative syndrome (EUS) collected from Mangalore, India, FTA and PCR could detect A. invadans in 100% of the samples compared to 89.04% detected by immunodot. FTA reagents were stable and produced expected results for 4 months when stored at 4~8°C. This rapid test could serve as simple and cost-effective on-site screening tool to detect A. invadans in fish from EUS outbreak areas and in ports during the shipment of live or frozen fish.