Vaccination and challenge.

SVCV-free common carp (~1.2 g) were used for vaccination. Fish were randomly divided into seven groups (100 fish per group): PBS, G131c (pEGFP-G131c plasmid), CHG (pEGFP-CHG plasmid), CS-PG, CS-PCHG, MCS-PG, and MCS-PCHG. All fish were vaccinated by intraperitoneal injection at a dose of 2 μg/g (body weight). Subsequently, the fish were transferred to different tanks and monitored daily.

For the challenge test, the water temperature was kept at 17 ± 0.5°C. Two independent challenge tests were carried out 28 and 70 days dpv, respectively. Each group of 50 vaccinated fish was randomly selected, transferred to new tanks, and intraperitoneally injected with 20 μL of 10² × 50% tissue culture infective dose(s) (TCID₅₀)/mL of SVCV. The survival rate was calculated after 16 days postchallenge.