05/06/14: Automated scanner to count parasites in farmed fish

SCIENTISTS in South Australia are developing an automated scanning technique for rapid and accurate counting of parasites on Yellowtail Kingfish.

The approach, developed by project leader Associate Professor Ian Whittington at the University of Adelaide, gives aquaculture managers a quick and cost-effective tool to maintain good health and optimise growth in their stock.

“External parasitic worms that infect the skin and gills of Yellowtail Kingfish are among the most serious health issues for the culture of this species,” said Whittington, who also holds a joint position at the South Australian Museum.

“This tool will assist in tracking and treating parasitic infection on Kingfish,” he said. “We’ve demonstrated our prototype to farm managers, and they’re excited about it.”

The current method for assessing Kingfish parasite numbers involves removing parasites from individual fish, then viewing under a microscope and counting one by one. The staff member must be trained to recognize each parasite species and life cycle stage.

The new method is faster and less reliant on trained staff, Whittington said.

“The approach relies quite simply on a Perspex tray placed on top of an ordinary flatbed scanner, a microscope and a specially-designed computer program. The parasites collected from the fish are separated into a single layer, the scanner collects an image of the worms and the program performs the analysis and sends the results to a spreadsheet,” he said.

Whittington’s innovative scanner may be one of dozens of aquaculture technologies discussed at the World Aquaculture Adelaide Conference and Tradeshow that begins in Adelaide on 7 June at the Adelaide Convention Centre.

Skin worms typically have a short and squat appearance, whereas the gill worms have a more cylindrical shape.

“Within about three minutes you’ve got an output about how many skin and gill parasites there are, as well as information on their length and width. You can then work out how many egg-laying adults you have, how many are on the verge of adulthood and how many are juveniles.”

Rapid assessment of parasite burden means that fish can be treated more effectively.

“With extra work, the program could also be tailored to count parasites in other farmed species such as tuna, barramundi and snapper,” added Whittington.

Yellowtail Kingfish and related species are an important global aquaculture species. 

In Japan fish are raised in cages after being wild-caught.

In South Australia, fish are hatchery reared in land-based facilities and then transferred into sea cages for maturation.

The cage-kept fish become infected with parasites due to contact with wild fish.

“Because the caged fish are stressed from being in a confined area, and their diet is not optimal – being comprised of pelletised food – the parasites with direct lifecycles can take hold and become established very quickly,” said Whittington.

A high burden of parasites can severely compromise the quality of the fish and reduce economic return.

“The skin parasites rasp away areas of the outer skin to cause lesions which are susceptible to secondary infections with fungi, microbes and bacteria,” he said. “The gill parasites suck blood, and cause anaemia. Together, the two cause ill health, slow down growth and can even lead to fish death.”

The project is being conducted with collaborators at SARDI Aquatic Sciences and the Institute of Aquaculture at The University of Stirling, Scotland.

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