Annual variability of infection with Cardicola forsteri and Cardicola orientalis in ranched and wild southern bluefin tuna (Thunnus maccoyii)

Infections by blood flukes from the genus Cardicola are the primary health concern in ranched bluefin tuna. This study explores annual variability of infection by C. forsteri and C. orientalis in ranched southern bluefin tuna (SBT) from Port Lincoln, South Australia, as well as in wild SBT caught at Pedra Branca, Tasmania. A hydrolysis probe-based qPCR assay was developed and validated for the quantification of C. orientalis, C. forsteri, and C. opisthorchis ITS2 rDNA. Having identified and confirmed C. forsteri and C. orientalis as the two species known to infect SBT the assay was used to quantify their ITS2 rDNA in SBT heart and gill samples from 2013 to 2015. Significant annual variability of infection in ranched SBT hearts was identified and C. orientalis was only detected in the 2013 samples. This study also presents the first detection of C. orientalis in wild SBT.

Significance:
- Validation of a hydrolysis probe-based qPCR assay for the detection and quantification of C. orientalis, C. forsteri, and C. opisthorchis ITS2 rDNA
- First detection of C. orientalis in wild SBT
- Significant annual variability in detection of Cardicola forsteri and Cardicola orientalis in ranched SBT heart from 2013, 2014, and 2015 harvests