A Case of Ulcerative Hemorrhage on the Body Surface of Largemouth Bass

doi:10.3969/j.issn.1004-843X.2025.12.030

Abstract：Largemouth bass has high breeding profit, no intermuscular bones, and delicious meat, which are deeply loved by breeders and consumers. With the rapid development of intensive and factory farming models, this fish has become one of China's main specialty freshwater aquaculture species, with a total national breeding output of nearly 1 million tons. However, with the continuous expansion of breeding scale and the increasing breeding density, bacterial diseases, viral diseases, parasitic diseases, fungal diseases, and non-pathogenic diseases have emerged one after another, seriously threatening the development of largemouth bass aquaculture. In recent years, the incidence of ulcerative hemorrhage on the body surface of largemouth bass has increased significantly near the selling stage, seriously affecting its survival rate and selling price. There are many types of causes leading to ulcerative hemorrhage on the body surface of largemouth bass, including mechanical injury, viral pathogens such as iridovirus, bacterial pathogens such as Nocardia, parasitic pathogens such as anchor lice, and fungal pathogens such as Saprolegnia. In October 2024, a largemouth bass fish population in a fish farm in Qionglai City, Sichuan Province, showed symptoms of ulcerative hemorrhage on the body surface. The staff immediately sent the dying individuals to the laboratory for clinical dissection and laboratory diagnosis. The detailed diagnostic process is as follows.