| Summary: | 碩士 === 國立海洋大學 === 水產養殖學系 === 91 === This study investigated the application of experimental vaccines prepared from Photobacterium damselae subsp. piscicida, originally isolated from diseased cobia, in the fish including the measurements of protective effects, the agglutinating of fish antisera, mucous killing assay, antibody titers and other immune index post vaccinaction.
Photobacterium damselae subsp. piscicida was virulent to the cobia ( 10g ) with an LD50 value of 1.03 × 104 CFU / g fish body weight. The treatment using inactivated extracellular products ( ECP ) to vaccinate the cobia for 2 weeks exhibited best protective effect after bacterial lethal challenge with a survival rate of 100%. In addition, this protective effect maintained until week 12, the end of the experiment. The other treatment using iron-regulated inactivated bacteria to vaccinate the fish for 8 weeks exhibited good protective effect with survival rates ranging from 83.3 to 91.7%. The treatments by immersion in cobia for 12 weeks did not show any good protective effect with survival rates ranging from 25 to 41.2%.
In antisera agglutinating tests, only treatments using inactivated ECP to vaccinate cobia exhibited high activities, followed by treatments with iron-regulated inactivated bacteria and immersion comparing to control. The killing activity of mucus obtained from cobia of all treatments were not obvious.
Cobia vaccinated with inactivated ECP exhibited high antibody titers ranging from 107 to 109. The high titers were also consistent at week 12 post vaccination. In addition, the liver and spleen of the cobia also exhibited high superoxide dismutase content and activities ( NBT assay ).
In summary, cobia vaccinated with inactivated ECP could possess strong protective immunity against Photobacterium damselae subsp. piscicida. The present results reveal that the inactivated ECP of Photobacterium damselae subsp. piscicida for future commercialized vaccine development against photobacteriosis in the cobia.
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