Susceptibility of swordtail, Xiphophorus helleri Heckel 1848, red platy, Xiphophorus maculatus Gunther 1866, sailfin molly, Poecilia Latipinna Lesueur 1821, and midnight molly, Mollienesia sphenops Cuvier and Valenciennes 1846, to Tetrahymena sp. from infected guppy, Poecilia reticulata Peters 1859

Guppy (Poecilia reticulata) is favoured by aquaria hobbyists due to their wide range of compatibility to other species of freshwater ornamental fish. Rearing multiple freshwater ornamental to other species together is a growing interest nowadays but will eventually lead to the possibility of disease and parasite transmission between the susceptible species. Tetrahymena sp. is the most notable parasite that seriously affects guppies. In this research, this parasitic protozoan was being used to evaluate the susceptibility of other freshwater ornamental fish to it in an experimental infection through co-habitation with infected guppies. In addition to guppy, Midnight molly, Mollienesia sphenops, Sailfin molly, Poecilia latipinna, and Swordtail, Xiphophorus helleri were susceptible, whereas Red Platy, Xiphophorus maculatus, was only susceptible after a prolonged period of exposure to the parasite. Temperature and pH measured during the experiment showed no significant to either the prevalence of infection or fish mortality. Prevalence of infection was significant with the fluctuation of dissolved oxygen, ammonia and alkalinity. Histopathology study showed that Tetrahymena sp. were found populating skin, muscle and gill of susceptible species. Aside from that, they were also found infecting internal organs which may suggest that Tetrahymena sp. were deeply penetrating muscle of susceptible freshwater ornamental fish species causing mortality of the susceptible species.