Ulcerative disease emergence in grass carp (Ctenopharyngodon idellus) aquaculture in China: Possible impact of temperature abnormality

Abstract

In 2019, an epidemic of ulcerative lesions emerged in grass carp (Ctenopharyngodon idellus) in the Yangtze River basin of China. Diseased fish displayed hemorrhagic ulcers of the tail muscle and reach 70% cumulative mortality, causing serious economic losses. The objective of the present study is to describe disease characteristics, analyze disease factors, and elucidate the etiology. Diseased fish from Qingbaijiang and Deyang, Sichuan, were dissected for the necropsy, pathology, and microbiology investigation. The histopathological examination revealed that the target organs of grass carp were muscle, spleen, and kidney, all showing severe necrosis and varying degrees of inflammation and edema. There were slight changes in the intestine, liver, gill, and heart. Nine strains of bacteria were isolated from diseased grass carp and were identified as belonging to four Aeromonas species. Subsequently, symptoms of tail muscle hemorrhage similar to the clinical symptoms were duplicated through re-infection. There was also a period of low temperatures in the affected regions in the early spring of 2019. Based on the results, we concluded that the genus Aeromonas was the pathogen causing the grass carp epidemic ulcerative disease, which perhaps links to the temperature abnormality.