Shedding Kinetics and Infection Stage-Dependent Horizontal Transmission of Infectious Spleen and Kidney Necrosis Virus (ISKNV) in Angelfish (Pterophyllum scalare).

Infectious spleen and kidney necrosis virus (ISKNV), a member of the genus Megalocytivirus, threatens ornamental and farmed aquaculture because of its broad host range and environmental persistence. This study investigated ISKNV infection dynamics and stage-dependent horizontal transmission in angelfish (Pterophyllum scalare). Immersion challenge experiments demonstrated that angelfish were highly susceptible to ISKNV infection, with cumulative mortality reaching 95% at 106 TCID50/mL. The estimated LD50 and ID50 values indicated that infection occurred even at sublethal viral concentrations. Viral loads peaked at 7 days post-immersion and were positively correlated with the severity of histopathological lesions in the spleen and kidney, including multifocal necrosis and enlarged basophilic cells. To assess horizontal transmission, naive fish were cohabited with infected donors for 24 h at different infection stages. These findings indicate that ISKNV transmission can occur following short-term cohabitation and that transmission outcomes may vary according to the infection stage of donor fish under the experimental conditions examined, providing insights into ISKNV transmission dynamics and the potential implications for disease management in the ornamental fish industry.