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Copi may be a great food source - for other fish

Asian carp
John Flesher
AP file
Copi may also appeal as a meal to other fish. That may create a new market for the invasive copi teeming in the Illinois and Mississippi rivers.

Illinois officials are marketing copi, the fish formerly known as Asian carp, as a tasty and nutritious food for humans to eat. But copi may also appeal as a meal to other fish.

That may create a new market for the invasive copi teeming in the Illinois and Mississippi rivers.

Yellow perch, and other popular food fish percids like walleye, are notoriously difficult to raise in captivity on fish farms. Newly-hatched percids are picky eaters. They greatly prefer live food to dry feed.

"This can be very problematic, because now we are raising these larval fish which are literally like babies," said Karolina Kwasek, a researcher at Southern Illinois University Carbondale. "You have to clean their tanks all the time maintain proper sanitary conditions. And you have a live food culture on top of them. So that becomes very time consuming, very labor intense and expensive."

That problem is compounded by the young yellow perch's poor swim bladder inflation. That means the fish spends more energy trying to float in the water. Those two factors lead to a high mortality rate for percids raised in captivity.

Kwasek is part of a team working to develop a dry food alternative for young yellow perch. Copi protein is ideal for this feed, but it's too large for the undeveloped digestive systems of larval perch to handle.

"We can't expect them to utilize efficiently a pelleted food that is composed of, say, fish meal that has the intact protein," said Kwasek. "But we can pre-digest it for the larva. So we can break that protein down into smaller components of smaller molecular weight that will be easily absorbed within the primitive digestive tract of the larva."

Kwasek's team concocted a slurry composed of muscle protein from copi and enzymes from the digestive tracts of adult yellow perch. That process breaks down the protein into tiny dry portions the percid larvae can easily digest.

Experiments to date have increased yellow perch survival rate into the juvenile stage from less than 10% to around 50%, with a swim bladder inflation rate of nearly 100%.

Kwasek said about 90% of the research conducted is easily replicable by fish farmers.

The research project will continue into 2023.

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Tim is the News Director at WCBU Peoria Public Radio.