Biostatic activity of piscine serum and mucus on myxozoan fish infective stages

► Fish serum impaired myxozoan sporoplasm cellular integrity, surface mucus did not. ► We found species specific differences in serum activity over incubation time. ► Host or host-related serum had significantly lower activity in two parasites. ► We could inhibit activity by bivalent ion withdrawal and heat inactivation.