When Jake Nelson went out July 18 on the fishing float below Lock and Dam No. 7, he got a surprise.
“I was fishing on the bottom for sunfish,” he recalled. “I had on a plain hook, red worm and a sinker.”
Jake got a bite, but the fish didn’t fight well.
“I thought it was just a sheepshead. I reeled it right off the bottom.”
What came out of the river looked a little like a piranha but without the pointed teeth. “It had teeth that looked almost like a human’s,” Jake said.
“The bottom teeth looked like our back molars.”
Jake’s dad turned to Fred Meyer, retired director of a U.S. Fish and Wildlife Service fisheries lab.
“(He) came to my house with a pail, asking if I knew what it was. I took a look and told him, ‘It’s a pacu,’” Meyer recalled.
Pacu hail from the Amazon and are becoming popular as aquarium fish. As a tropical species, they aren’t supposed to be able to survive in the upper Mississippi. However, the owner of the fishing float told Jake the fish he caught was the fourth one of that type he has seen this year.
Mark Steingraver, a U.S. Fish and Wildlife Services fisheries biologist, said he’s not surprised.
“They’re probably aquarium releases … that’s my take on it. We’ve seen this going on for more than a decade, especially with these pacu,” he said. “They’re caught all across the nation. Quite often what happens is that pet retailers market pacu, and I have the feeling that the public is not fully aware of the size these fish will grow to.”
Pacu can reach 12 to 14 inches in less than a year, Steingraver said, outgrowing small tanks. They often reach 2 feet in length, and 30-inch fish topping 50 pounds have been documented.
“They wouldn’t do well in the Mississippi in the winter time,” Steingraver said, “but they could perhaps make it through the winter if they find a thermal effluent, such as a power plant or a sewage treatment plant. Generally I wouldn’t expect them to survive or reproduce here.”
The real danger that imported tropical fish pose is they could potentially carry parasites, bacteria and viruses to native fish, Steingraver said.
“Fish that are brought into this country for hobby purposes come from all over the world,” he noted. “If they are released into our public waters, these disease pathogens could potentially spread to our native fish, with dire consequences.”
Case in point: viral hemorrhagic septicemia virus (VHS).
“We don’t know how it got here, but it’s having major ramifications throughout the Great Lakes states, to the point where it’s very difficult to get permission to move fish from one state to another,” Steingraver said.
VHS is killing native fish including large muskies, he noted.
“(VHS) is assumed to be in the Mississippi River drainage, but it hasn’t been detected as of yet,” Randy Hines said.
Wildlife Biologist Hines works at the Upper Midwest Environmental Science Center on French Island. He said boat owners are encouraged to drain their live wells and bilges and let them stay that way for at least
72 hours before going to another area. The same applies to fishermen’s waders, since VHS can survive out of the water for that length of time. An alternative is to disinfect with 10 percent bleach water, he added.
Eleven research teams work at the science center, and diseases that affect native fish are one area of study, Hines said. Another is invasive species, including Asian carp, which are poised at the doorstep of Lake Michigan, moving up the Mississippi and Illinois rivers.
Locked securely away in the bowels of the research lab on French Island are tanks containing silver and bighead carp. Hines said they are being used to develop “integrated pest management” control measures, including targeted pesticides that are species-specific. An example of this could be an enzyme that would only affect the ability of Asian carp to digest food. It’s called bio-technology.
Silver carp were imported to clear up nutrient-rich ponds and wastewater treatment plants. Bighead carp were stocked into catfish farms to improve water clarity. Both are filter feeders. Hines said silver carp feed on extremely fine particles, including zooplankton, phytoplankton, bacteria and detritus. Bighead carp feed on somewhat larger plankton. Both are voracious feeders, capable of consuming up to 40 percent of their body weight in a day.
“These guys have the ability to out-compete our native fish,” Hines said. “They take food off the bottom of the food chain. That’s the biggest ecological damage. … When you look at the Illinois River, 80 percent of the biomass, or weight of fish, is carp. That includes common carp, plus silver, bighead and grass carp,” he said. “Only 20 percent is native fish. In the Mississippi down around
St. Louis, 50 percent of the biomass is carp.
“They were found here a year and a half ago,” Hines said. “Commercial fishermen found bighead carp and one single silver carp in pool 8, right here by La Crosse.”
Hines said zebra mussels are another example of an aquatic invasive. They’re widespread in the Mississippi, with populations that have cycled up and down over the years. Right now, they’re on an upswing, and research teams are looking for control measures to stem the tide. Extermination of zebra mussels is beyond current science, he said.
“In every other country that’s been struck with them, no one’s ever been able to get rid of them,” Hines said.
The labs work on, with multiple levels of disinfection ensuring that no species or pathogens escape.
“All of our fish are for research purposes,” Hines explained. “None will ever be released. The facility has the ability to raise cold, cool and warm-water fish, and can even mimic the type of water found in any drainage in the world in terms of acidity, mineral content and more.”
It’s not all bad news, either. Swimming in a tank in the native species section of the facility are pallid sturgeon, which are being studied in an effort to re-establish them in their historic range, including the upper Mississippi.
The lessons of history are sobering when it comes to invasive species, however.
“There has been no silver bullet for any invasive species,” Hines said. “We need integrated pest management. We need to be able to control invasive species through a series of different kinds of limiting methods and tools so that we don’t see these issues expanding and becoming too bad.”