New Method Tests Reproductive Potential Of Asian Carp

By on August 27, 2015
The crew of the S.S. Minnow electroshocks grass carp from a triploid standing stock at Cleveland Metroparks Zoo. (Credit: Katherine Krynak)

The grass carp was introduced to waterways throughout the U.S. to clear out ponds fraught with weeds, but this and other Asian carp species has proven to be a formidable nuisance capable of overtaking indigenous populations.

Luckily, hatcheries that raise these species shock the eggs with water pressure shifts, producing a third chromosome set in eggs and rendering their fry sterile so that the adult fish can be used for habitat management. A new study out of Case Western Reserve University has produced an innovative method for testing whether an invasive Asian carp is diploid or triploid — that is, possessing two or three sets of chromosomes.

Using blood samples, the method can quickly and accurately determine a fish’s reproductive capabilities, all at a fraction of the cost of previous techniques. The study began as a research paper by CWRU graduate student Katherine Krynak — who has since completed her doctoral studies — for an ichthyology class taught by Ron Oldfield, an instructor in CWRU’s department of biology.

“I was playing around with different ideas, figuring out what I wanted to do,” Krynak said, noting that most of her studies have focused on amphibians.

While poring over scientific literature for a method of differentiating carp species, she came across a Chinese study showing that hybridized goldfish with extra chromosomes had higher counts of red blood cells with abnormally shaped nuclei.

Krynak and Dennis extract blood samples from triploid grass carp for blood smears. (Credit: Katherine Krynak)

Krynak and Dennis extract blood samples from triploid grass carp for blood smears. (Credit: Katherine Krynak)

“It was kind of a roundabout way to stumble across this project,” Krynak mused. “It’s far out of my realm of expertise, but it seemed like an interesting question that we could identify and find an answer for.”

The first iteration of the study took place at a Cleveland Metroparks lake with help from Cleveland Metroparks staff and Pam Dennis, a Metroparks zoo scientist. The researchers used electrofishing to round up every grass carp in the lake, then drew blood samples from each fish. Further sampling was conducted at Keo Fish Farm.

Basing her method on the Chinese paper, Krynak checked the samples for red blood cells with unusual nuclei. To inspect the samples, the researchers smeared a drop of fish blood on a glass slide, preserved it with methanol and then dyed the slide so that any abnormal nuclei would be made apparent under a microscope.

“Just glancing at these slides, you can tell if these are diploid or triploid grass carp,” Krynak said. “It’s overwhelmingly easy to differentiate.”

Though Krynak is pursuing other studies as a postdoctoral researcher at CWRU, she’s glad that Oldfield is teaching the method she helped develop in his course, and is excited for its potential overall.

“I’m extremely happy that this could be used to help conservation initiatives for removing fertile grass carp from the Great Lakes region,” she said.

Top image: The crew of the S.S. Minnow electroshocks grass carp from a triploid standing stock at Cleveland Metroparks Zoo. (Credit: Katherine Krynak)

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