LondonDragon said:
It mat actually depend on the species. I have one 1996 journal extract issued by a crew at John Hopkins University (Graczyk/Fayer/Cranfield) whose data indicate that C. parvum inoculated fish, lizards and snakes revealed no life cycle stages of this protozoan in any section of the digestive tract at 7 days post inoculation and 14 days post inoculation, even though by day 4 PI fecal specimens of all inoculated tested oocyst positive. The conclusion of that study was that no gastrointestinal infection was possible in lower vertebrates although they may retain the oocysts.
In a 2007 report by Méndez-Hermida1/Gómez-Couso/Ares-Mazás University of Santiago Spain, their data clearly indicates gastrointestinal infection in Guppies after an inoculation of Cryptosporidium molnari and Cryptosporidium scophthalmi. An abstract of the report can be found here:
transmission of cryptosporidiosis in cultured fish
What is noteworthy of that report is that the method of inoculation was by infected Artemia (Brine Shrimp). The implication here is that the transmission of the protozoan can easily occur by infected food sources as well as by infected water supply. Also noteworthy is that although histopathological damage was detected in this infection, no clinical/external symptoms were noted in the marine fish in which C. scophthalmi was isolated. Presumably, cryptosporidiosis effects would be short term diarrhea, dehydration and stomach cramps (at least that's what it is in humans).
Cheers,