Study on optimum size of a hybrid catfish for the application of Aeromonas hydrophila vaccine by immersion method
1994
Chalida Chamanon
Hybrid catfish with four different weights were immunized with vaccine prepared from formalin-killed Aeromonas hydrophila by hyperosmotic and direct immersion. After challenging with virulent bacteria, immunized hybrid catfish with average weight of 2.45 and 1.39 gms had significantly lower mortality rate than 0.65 and 0.17 gm fish with the average values of 45.48, 46.52, 60.15 and 62.22 percents respectively. Vaccinated hybrid catfish with average weight of 2.45 gms had the highest relative percent survival (RPS) with the average values of 34.43 percents and 28.99, 23.08 and 17.05 percents for the respective smaller fish. As far as the mode of vaccination is concerned, hyperosmotic immersion in 1.5 percent saline solution for 2 minutes followed by 1 hour immersion in vaccine produced the lowest mortality and highest RPS after challenging with virulent Aeromonas hydrophila with the average values of 38.00 and 45.57 percents respectively. Hyperosmotic immersion showed significant advantage over the direct one with the same length of vaccination period. Furthermore, this mode of immersion did not cause any stress to the fish judging from the growth and survival rate of the vaccinated fish. It is clearly shown from this study that hybrid catfish with weight over one gram had significantly better response to Aeromonas hydrophila vaccine than the smaller fish. Hyperosmotic immersion in 1.5 percent saline solution for 2 minutes followed by one hour vaccination induced the better response than other modes of vaccination.
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