RMIT developing safer approach to parasite diagnostic testing of Australian tuna

Southern Bluefin Tuna (Photo: Australian Marine Conservation Society)

RMIT University researchers are working with Australia’s tuna industry to develop a novel diagnostic testing technique for application on water, to assist tuna farmers to make informed decisions about managing the health of their stock.

Researchers are developing a new test for two tiny parasites that threaten Australia’s ranched Southern Bluefin Tuna, and are working with industry to develop best practice for treatment.

The first findings from the collaboration, published in the Journal of Aquaculture, revealed the effectiveness of targeted treatments of ranched tuna and a reduction in parasite numbers. These husbandry techniques are widely used in fish farming worldwide under veterinary supervision and have been recognised as one of the many reasons behind the high productivity of Australian tuna ranching.

The parasitic blood flukes, Cardicola forsteri and Cardicola orientalis, asexually reproduce in a polychaete worm found on the sea floor before emerging to infect tuna. This can be deadly for the species if left untreated.

Though naturally occurring in approximately five percent of wild tuna, the parasites are of particular concern for fishers who capture and keep fish alive for ranching in areas where the polychaete is more common.

RMIT lead researcher Dr Nathan Bott said that current diagnostic testing methodology is fatal and involves taking samples from the tuna’s gills, blood, and internal organs, thus the need for new methods to enable accurate samples to be taken without harming live fish.

The research team hopes to develop a new portable diagnostic test that would only require a mucus swab from the gill of a live fish to test for the presence of the parasite.

The parasite found in tuna is restricted to the fish’s circulatory system and cannot transfer to humans.

However, the parasite could lay eggs that enter the fish’s blood stream and lodge in the gills, which in turn could cause respiratory failure that can be fatal. The resulting blood flukes can cause mortalities, which Dr Bott believes will adversely affect the tuna industry.

The research will also make recommendations on best practice for managing the handling of fish once caught to reduce any effects the parasite may have.

The RMIT research team hopes that improved diagnostic testing would help provide more accurate guidelines for when to treat affected fish, reducing the cost of treatment and lowering mortality.

The study is being undertaken by researchers at RMIT University in collaboration with the Australian Bluefin Tuna Industry Association (ASBTIA) and the Fisheries Research and Development Corporation.

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