First outbreak of trypanosomiasis in farmed blood parrot cichlids (Vieja melanura♀ × Amphilophus citrinellus♂) from southern China.

Outbreaks of fish trypanosomiasis are regularly reported in cultured groupers (Epinephelus spp.), largemouth bass (Micropterus salmoides), and many other species of Cyprinidae, but only rarely reported in ornamental fish. This study reports a trypanosomiasis outbreak in farmed blood parrot cichlids (Vieja melanura ♀ × Amphilophus citrinellus ♂) in the Nansha district, Guangzhou, Guangdong province. From May 2021 to January 2022, up to 100 fish died daily with an estimated overall mortality of 20%. Blood samples were collected from 21 sick fish, characterized by reduced feeding, slow movement and swimming close to the surface of the water, and 5 asymptomatic fish for parasite examination. Wet blood mounts and Giemsa-stained smears showed that trypanosomes were found in 20 of 21 sick fish (95.2%) and 4 of 5 (80%) asymptomatic fish. Parasitemias were recorded at levels of up to approximately 108 trypanosomes /ml of blood. Morphological and genetic analysis showed that the trypanosome infecting blood parrot cichlids was Trypanosoma carassii danilewskyi. In addition, histopathological analysis showed a severe steatosis in liver and an aggregation of pigments in the spleen and kidneys, which are likely to be melanomacrophages. To our knowledge, this is the first report of an outbreak of trypanosomiasis found in farmed blood parrot cichlids. • The first outbreak of trypanosomiasis caused high mortality in farmed ornamental fish. • Trypanosoma carassii danilewskyi is highly prevalent in both sick fish and asymptomatic fish. • Trypanosomiasis is linked with severe steatosis and melanomacrophage aggregation. [ABSTRACT FROM AUTHOR]