First case of chronic systemic spironucleosis in Freshwater Angelfish (Pterophyllum scalare Schultze, 1823) in Türkiye

This study aimed to identify the cause of sustained mortality in freshwater angelfish (Pterophyllum scalare Schultze, 1823) kept at an ornamental fish production facility in Türkiye. Parasitological, bacteriological and histopathological examination were performed on moribund hybrid angelfish individuals. The moribund fish had haemorrhaged eyes, darkened skin, scale loss, ascites and false faeces. A pale liver, splenomegaly and a thinning of the intestinal wall were observed internally. The parasitological examination revealed flagellated protozoan endoparasite Spironucleus sp. in the intestine. A number of histopathological changes were observed including lipid degeneration in the liver, hemosiderin deposits as well as granulomas in the spleen, a large number of mast cells in the lamina propria of the intestine and enteritis. Numerous Spironucleus parasites were seen in the intestinal wall. According to physiological and biochemical tests, the bacterial isolates obtained from the visceral organs of some fish were identified as Citrobacter freundii. After oral metronidazole treatment, with a dose of 50 mg/kg fish daily for 5 days, a decrease in fish mortality and resumed feeding were noted. A chronic spironucleosis, which systemically affects fish by penetrating the intestinal mucosa, was identified as the cause of this sustained mortality in freshwater angelfish.