Pathological characterization and cause of a novel liver disease in largemouth bass (Micropterus salmoides)

Abstract

With the rapid development of intensive aquaculture in recent years, liver disease of largemouth bass has been increasingly prominent both in China and even around the world. The main gross pathology found the liver is swollen, pale or white in color, with round and blunt edges, and brittle texture. The morbidity and mortality varied. In some cases, the cumulative mortality could reach more than 20%. To investigate the etiology of largemouth bass, histopathological and ultrastructural pathology were performed. The results showed that diseased fish expressed fat accumulation around the pyloric caeca, and the liver showed hepatomegaly with extensive yellowish or whitish color. Hepatocytes had degenerated vacuoles that were different from fatty liver disease. Large number of irregular vesicles that accumulated in hepatic cells which contained a mass of glycogen-like granules and myeloid bodies. This novel liver disease was a common phenomenon in the culture of largemouth bass. The animal feeding experiment was to investigate the causes of the disease, and the results confirmed that a high carbohydrate diet was one of the causes of novel liver disease of largemouth bass. Additionally, blood biochemical indexes suggested that the disease can cause systemic metabolic disorder. Overall, the results demonstrated that the death of a large number of largemouth bass was caused by novel liver disease, due to a high carbohydrate diet.

Keywords

• Histopathological
• Largemouth bass (Micropterus salmoides)
• Ultrastructural pathology
• Glycogen-like granule
• Irregular vesicles