Detection of scale drop disease virus from non-destructive samples and ectoparasites of Asian sea bass, Lates calcarifer

Non-destructive sampling methods offer practical advantages to detection and monitoring of viral pathogens in economically important farmed fish and broodstock. Here, we investigated whether blood, mucus and fin can be used as non-lethal sample sources for detection of scale drop disease virus (SDDV) in farmed Asian sea bass, Lates calcarifer. Detection of SDDV was performed in parallel from three non-destructive and seven destructive sample types, collected from both clinically sick fish and subclinical fish obtained from an affected farm. The results showed that SDDV was detectable in all 10 sample types with the percentage ranging from 20% to 100%. Blood was the best non-destructive sample source exhibited by the fact that it yielded 100% SDDV-positive tests from both sick (n = 12, 95% CI: 69.9-99.2) and clinically healthy fish (n = 4, 95% CI: 39.6%-97.4%) and is considered a sterile sample. This study also revealed concurrent infection of SDDV and two ectoparasites Lernanthropus sp. and Diplectanum sp., in all affected fish (n = 8, 95% CI: 46.7-99.3) during the disease outbreak. These ectoparasites also tested positive for SDDV by PCR, indicating that they were potential sample sources for PCR-based detection of SDDV and possibly other viruses infecting Asian sea bass.

Automated summary

Non-destructive sampling methods are beneficial for detecting and monitoring viral pathogens in economically important farmed fish. Blood was found to be the best non-destructive sample source for detecting scale drop disease virus in farmed Asian sea bass.