ELKHART — You never know what you might find in the St. Joseph River.
The Elkhart Public Works Department discovered an orange and white koi during spring sampling near Indiana University South Bend.
“This is kind of a rare find for us. This is maybe the second or third koi. We’ve also encountered maybe a dozen goldfish over the years,” said Daragh Deegan, the city’s aquatic biologist. “One time, we found a goldfish over 14 inches long. It got really big in the river.”
As a nonnative species, koi generally find their way to local waters incidentally. Deegan said he believes it’s possible this one came from a pond that overflowed during last year’s flooding, or slid through connector pipes on a retention pond that drained into the river. He said it might happen more often than anyone knows.
“I speculate a little bit that because they’re bright fish, and there’s no other fish out there like them, that the predatory fish pick off the smaller ones quickly.”
Interns with the public works department on Thursday captured nearly 20 species of fish, including the massive koi, but it escaped before they could measure it.
Koi, a member of the carp family, are an invasive species, but Deegan said carp have become so pervasive that many people do not realize they are nonnative.
“They were brought to the United States for food and spread across the country. There’s nothing I can do about it,” Deegan said. “One of the problems with invasive species is they reproduce prolifically. They reproduce in such large numbers that there’s no way to get a handle on it.”
Large carp – and large koi – however, can create issues because they grow so large. If they survive the first few years of their decades-long life, predators such as bass and pike cannot keep them under control.
“Being a nonnative fish, they use the resources of other fish. They cause damage to nests and disturb the habitat of our other fish species,” Deegan said.
Carp can grow to be up to 50 pounds and can live for nearly 20 years, he said.
“Koi in the river breed with other carp in the river and share their traits but we already have a bunch of carp in the river,” Deegan said.
Offspring would be less colorful than their koi parents, he said.
It’s not entirely uncommon for nonnative fish to be found in the rivers around Michiana. They come from private owners’ backyard ponds, or even aquariums. One year, the department captured a red belly pacu, a nut-eating fish from the Amazon that can grow to up to 2 feet long, near Central High School.
“Fish like that, these unusual tropical species, they’re from warm climates. It’s very unlikely they survive the cold winters of Indiana,” Deegan said. “Koi on the other hand are able to adapt to the colder climate.”
In conjunction with the South Bend Public Works Department, Elkhart has been sampling for about a month now, though the wet weather has made for rough waters, so it’s been tough to gather samples. As a result, Deegan said the numbers of fish collected this year have been lower than usual but still within standard deviation.