This thesis examined potential mechanisms responsible for mediating anorexia associated with the disease cryptobiosis. Rainbow-trout ('Oncorhynchus mykiss') were treated with both the pathogenic and attenuated vaccine strain of 'Cryptobia salmositica,' as well as fed equal rations to that of infected fish. At the time of acute disease, anorexia was positively correlated with a reduction in O2 carrying capacity. Increases in corticotropin-releasing factor (CRF) and urotensin 1 (UI) mRNA levels were also observed at this time, but these changes did not correlate with those in food intake. Interteukin-1 beta (IL-1[beta]) mRNA levels in both the head kidney and spleen were significantly reduced in infected fish compared to nai?ve controls. Moreover these changes in gene expression were not affected by fasting. Lastly, neither plasma cortisol or adrenocorticotropin hormone (ACTH) levels were affected by cryptobiosis. Taken together, these results suggest hypoxaemia is a likely mediator of said anorexia, however the mechanism appears to be independent of the anorexigenic actions of CRF, UI, IL-1[beta] or cortisol.