Objective Hybrid snakehead is an important special aquatic fish in China. In order to find out the infection status of hybrid snakehead rhabdovirus (HSHRV), the rhabdovirus disease of hybrid snakehead cultured in the Pearl River Delta was investigated from March 2021 to February 2022.

Method The parents, fry and water samples of hybrid snakehead were randomly sampled in breeding stage, and these were randomly sampled at fixed time in culture stage and sampled when the outbreak of the virus. A total of 333 samples were collected during the whole monitoring period. Mixed samples of mung bean-sized liver, spleen and kidney were stored in liquid nitrogen for RNA extraction. And reverse-transcribed cDNA was used as template to detect rhabdovirus by real-time fluorescence quantitative PCR (qPCR).

Result The main clinical symptoms of rhabdovirus-infected fish were that the fish swam irregularly and spin. Although there was no obvious symptom on the body surface, the liver, spleen, kidney, intestine and swim bladder became red or swollen. The qPCR results revealed that the average positive rate of HSHRV was 13.21%, which was mainly detected from April to November. Among them, the positive rate of samples detected in August was as high as 23.91%. The average positive rate of HSHRV in the culture stage (17.01%) was significantly higher than that in the breeding stage (3.26%). In terms of fish body size, 32.20% of the fry were most susceptible to HSHRV infection within 10 cm, mainly detected from March to September, while 9.52% of the fish of more than 20 cm were least susceptible to HSHRV infection.

Conclusion The positive rates of HSHRV in hybrid snakehead in breeding stage and cultivating stage as well as in different size are determined, which provide references for further understanding the epidemic regularity of hybrid snakehead rhabdovirus disease, with a view to providing data support for the prevention and control of hybrid snakehead rhabdovirus disease.