Artificial Infection Pathway of Largemouth Bass LMBV and Identification of Resistant and Susceptible Individuals

Identifying disease-resistant and disease-susceptible materials in largemouth bass can provide fundamental analytical information for disease-resistant breeding research on this species. To date, no stable and effective artificial infection pathway has been established against largemouth bass virus (LMBV) in largemouth bass. In this study, using the pathogen at a concentration of 1.60 × 105 TCID50/mL, largemouth bass juveniles were infected using three different methods: muscle injection, feeding, and immersion. A comprehensive comparative study was conducted on parameters such as disease progression, viral load, pathological changes, and electron microscopy. The results revealed that the injection group experienced rapid mortality, with all individuals dying within 6 days after the infection. The feeding group showed minimal mortality, with an overall mortality rate of 28.57%. The immersion group reached its peak mortality on the 9th day after infection, with an accumulated mortality rate of 63.24%. Viral gene quantification results showed that while in the injection group muscles had the highest viral load followed by the liver and spleen, the other infection methods led to the highest viral loads in the liver and spleen. Tissue pathology and electron microscopy observations revealed that the liver and spleen exhibited the most significant pathological changes and were the easiest organs to detect viral particles, indicating that the liver and spleen are the primary target organs of LMBV in largemouth bass. In conclusion, this study suggests that immersing largemouth bass in LMBV at a concentration of 1.99 × 103 c/mL (diluted 80 times) closely mimics the natural infection rate, allowing for a clear differentiation between causes of death and survival, making it an almost non-invasive artificial infection method that closely resembles natural infection conditions. These findings can provide crucial support for the accurate identification of disease-resistant and disease-susceptible materials in largemouth bass and the breeding of disease-resistant varieties.