Since the recent finding that mucus-derived nucleosides serve as the key host cues for myxozoan actinospore fish host recognition, their use for experimental actinospore activation in the laboratory or application in disease prevention has not progressed yet. One obstacle has been the low solubility of pure inosine and guanosine. To overcome this, we used inosine-arginine salt, which was found to incorporate both high activation properties and high solubility. We tested its efficacy both in microassays directly observing reactions of actinospores of two distantly related myxozoan species, Myxobolus cerebralis and Myxobolus pseudodispar in comparison to inosine, as well as its actinospore-inactivation properties by preliminary polar capsule discharge in an infection experiment. The substance was considerably more effective in eliciting polar capsule discharge and sporoplasm emission at much lower concentrations than pure inosine and, in contrast to the latter, remained dissolved in aqueous solution. Ionsine-arginine exposure of M. pseudodispar actinospores apparently resulted in polar capsule discharge and sporoplasm emission before host contact and subsequently in a lower infection rate in roach, Rutilus rutilus
