Pacific bluefin tuna has one of the fastest growing aquaculture industries due to its high price and strong demand. However, in recent years, farmed juvenile Pacific bluefin tuna in Japan have been affected by parasites, leading to high mortalities, writes Lucy Towers, TheFishSite Editor, live from 'Aquaculture 2013: To the Next 40 Years of Sustainable Global Aquaculture' conference, in Gran Canaria, Spain.
The two different parasites affecting Pacific bluefin tuna are cordicola orientalis, which affects the gills and cordicola opisthorchis, which affects the heart, stated S. Shirakashi, Kinki University, Japan, during his presentation.The parasites lay eggs which accumulate in the gill lamellae and clog blood vessels, therefore causing high mortality among juveniles.Dr Shirakashi stated that tuna showed no sign of infection in the hatchery but did once transferred to sea cages.
He also observed that no, or low, infection was seen after seven months.
In order to find a treatment for Cordicola, Dr Shirakashi trialed Praziquantel (PZQ) in various doses. After being administered orally for three days, PZQ killed the majority of worms. The number of eggs also declined, but only in the higher dose. Overall, Dr Shirakashi stated that a minimum dose of 3.75 - 7.5 mg/kg BW/D is needed in order to be effective. He also noted that the drug proved safe to use and effective after only a short exposure. As the drug has not been approved for use in the treatment of cordicola, an application for approval has now been sent to the Japanese government.
Via John Bostock