The study on diplomonad flagellates infection in some ornamental fishes in the family cichlidae i.e., angelfish (Pterophyllum scalare), oscar (Astronotus ocellatus), blue mbuna (Labeotropheus fuelleborni) and the family osphronemidae i.e., Siamese fighting fish (Betta splendens) revealed that this parasite infected three out of four ornamental fish species, angelfish, oscar and blue mbuna. The highest infection was recorded in angelfish (90%) followed by oscar (75.4%) and blue mbuna (61%), respectively. Identification of diplomonad flagellates from angelfish by means of morphological studies under light and electron microscopes indicated that the parasite was Spironucleus vortens. The 14–days LD50 of S. vortens in angelfish was 2.99x103 cells. Histopathological changes of infected angelfish revealed granulomatous liver, numerous numbers of melanomacrophage in the spleen and inflammation of the intestine. Susceptibility study of S. vortens to goldfish (Carassius auratus), guppy (Poecilia reticulata) and platy (Xiphophorus maculatus) indicated that they were resistant to artificial infection. In vitro examination of the growth inhibition assay of S. vortens indicated that dimetridazole and metronidazole were effective in inhibiting parasite growth after 48 hrs exposure at concentrations of >4.0 µg/ml and >6.0 µg/ml, respectively. Magnesium sulfate at a concentration of >60 mg/ml inhibited the parasite growth after 72 hrs exposure. In vivo examination of the dimetridazole efficiency on S. vortens infection indicated that dimetridazole at 4.0 µg/ml provided the highest efficiency which could be used for treatment of spironucleosis in angelfish.
