Small snails pose big problems for native fish

Scientists studying invasive snails in local waterways

SAN ANTONIO – A small snail from Asia is causing big problems for some fish in Central Texas rivers and lakes and researchers are trying to find a way to stop the snails from spreading.

Texas State University Biology Professor David Huffman said the invasive species of snail was introduced into local waterways by people dumping unwanted pet fish into rivers and streams.

"You know they got started here from aquarium dumps," Huffman said.

The snails were first discovered in the San Antonio River and have since spread to the Comal and Guadalupe rivers as well as Lake Dunlap and Lake McQueeney.

Huffman said the snails were first discovered in the spring-fed Comal River in the 1990's.

Researchers like Huffman once believed the snails would be contained to the Comal because they are sensitive to colder water.

"In experiments in the lab, they haven't been able to survive and reproduce at sustained temps below 18 degrees Celsius (64 F)," Huffman said. "So we thought the rest of the fish were safe from this and that the springs would be impacted, which is very unfortunate, but we figured the rest of the springs were safe, until now."

Huffman said he recently found hundreds of the snails thriving in much colder waters.

"I found them just two weeks ago, at Dunlap Dam, hundreds of them that were like 3-year-old snails, were thriving in temperatures that were clear down to 12 and 13 degrees Celsius which is supposed to kill them overnight," Huffman said.

Researchers now believe the snails have evolved to survive and thrive in the colder waters which means it could make it easier for them to spread to other waterways.

"If they can survive in the Guadalupe, then they can survive in most of the streams in Central Texas," Huffman said. "Because these snails are so hardy, it's quite possible that they'll be transported on boats, or heaven forbid my own nets, going from one place to another, or boots or wading shoes for tubers coming down the river and going back up and that sort of thing."

While the snails themselves are highly competitive and can overtake native snails, they pose a bigger problem.

The snails are also hosts for a parasite that can be deadly to some native fish, including the endangered Fountain Darter fish.

"Not all fish are infected. About half of the species of fish that are exposed are going to be affected to some degree," Huffman said. "Some of them are affected dramatically. It just almost destroys their gill tissue so they can't breath."

Huffman believes the parasites are the reason why there aren't as many large fish in the rivers.

"Where the Comal flows in and brings all these parasites onto the Guadalupe, there are very few nice bass and hardly any nice minnows in there and relatively few sun fish," Huffman said.

Huffman and other scientists are continuing to research the snail and the parasites to see how they are spreading and affecting the local fish. He said the snails are hard to kill and right now no one knows how to get rid of them.

"The main thing is to try to keep it from spreading to other places and so it may be necessary to implement some kind of measures to at least inhibit the rate at which it spreads," Huffman said.

While the snails are known to carry some parasites that can affect humans in other parts of the world, Huffman said none of those parasites have been found here and he believes the fish in the rivers are safe to eat and it's just as safe to swim in the water.

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