TRIALS WITH AN ORALLY AND IMMERSION-ADMINISTERED BETA-1,3 GLUCAN AS AN IMMUNOPROPHYLACTIC AGAINST AEROMONAS-SALMONICIDA IN JUVENILE CHINOOKSALMON ONCORHYNCHUS-TSHAWYTSCHA

A study was conducted to examine the effectiveness of a commercially a vailable beta-1,3 glucan, VitaStim-Taito (VST), to stimulate immunity in juvenile chinook salmon Oncorhynchus tshawytscha against the bacter ium Aeromonas salmonicida (As) causing furunculosis in salmon. VST had earlier been shown to be capable of elevating the potency of an anti- furunculosis vaccine when administered by injection. In the present st udy, 2 routes of administration were evaluated for their effectiveness : oral delivery and immersion. In the oral administration trials, VST in its crudest form was mixed (without the As vaccine) into a steam-pe lleted diet at a rate of 0, 0.01, 0.1, and 1.0%. The 4 diets were fed to Lest fish at 2% of body weight d(-1). After 7 d on the diets, the f ish were bath-challenged with As, the fish being maintained on the tes t diets for the rest of the experiment. VST added to the diet at eithe r 0.1 or 1.0% resulted in significant protection against the As challe nge. In the immersion trials, an As vaccine was administered to the Le st fish either alone or in combination with a pure or a crude form of VST. The vaccine and the VST were also administered alone. Following a bath challenge with virulent As at 21 d post-vaccination, no signific ant protection was noted in any of the groups tested, indicating that VST was inactive as an immunopotentiator by this route. The fish were, however, immunocompetent because protection occurred when they were i njected with the vaccine alone.