Abstract
In this pilot study, juvenile rainbow trout were experimentally challenged with the microsporidian Loma salmonae to determine the effects of immunostimulation with β-1,3/1,6 glucan administered in the feed at 200 mg/kg of feed, and immunosuppression with dexamethasone at 300 mg/kg of feed when these were administered in the early stages of infection. Six weeks after oral exposure to Loma spores, control fish developed a mean of 34.8 spore filled xenomas per gill arch; those which had received β glucan had significantly fewer xenomas (23.6) whereas those receiving dexamethasone had significantly more (43.0). Paradoxically, when fish received both β glucan and dexamethasone in any of three temporal combinations, xenoma numbers were significantly higher (51.0-65.1) even when compared to fish receiving only dexamethasone.
