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Don't Dump That Aquarium

Cute aquarium fish become ugly monsters in springs and streams.

By Larry D. Hodge

It’s an annual rite of spring in San Marcos: College students heading home for summer or off to a new job discard dorm-room detritus in a frenzy of packing and moving. Much unwanted stuff goes into dumpsters. Unfortunately, some aquarium contents go into the San Marcos River.

Other people have fish that have outgrown their aquarium and, in an act of misguided kindness, release them into the nearest stream or pond.

“People have fish in their aquariums they don’t want to kill, so they dump them into a pond, river or spring,” says Tim Bonner, assistant professor of biology at Texas State University. “They may save the life of one fish, but in doing so they could wipe out a whole population of native fishes.”

Bonner and TPWD fisheries biologist Gary Garrett are particularly concerned with impacts on native fishes — some of which are threatened species — from a South American import commonly known as armored catfish or armadillo del rio. This creature (Hypostomus plecostomus) is undeniably cute — and useful — as it vacuums algae off aquarium gravel. But when you place that same fish into a spring-fed stream, it turns into an ecological disaster. Armored catfish can grow to a foot long, and because they are covered with bony armor plate, almost nothing can eat them. They wipe out algae that other fish depend on for food. Worse yet, as they vacuum the bottom clean, they eat eggs of other fish and keep them from reproducing.

Heard enough? There’s more. When these invaders spawn, they burrow into river banks, not only making the bank unstable but also releasing sediments that can adversely affect other fish species as well as plants such as wild rice.

The San Marcos River isn’t the only body of water with an armored catfish problem. Bayous in the Houston area are infested, as is the San Antonio River. “Spring-fed streams are where we have the most problems, because the water stays the same temperature year-around and does not get cold enough to kill them,” says Bonner.

What harm can there be in dumping one little fish into the river? Garrett’s research in Del Rio provides the answer. “In San Felipe Creek in 1997, we found four of them. Now there are hundreds of thousands of them. These things explode,” says Garrett.

While it is legal for dealers to sell the exotic species, it is against the law to release them into public waters. That puts responsibility for controlling the problem squarely on the shoulders of aquarium owners. “We have tried everything from electroshocking to baited traps, and we have not been able to impact them,” says Garrett. “We will begin a research project this summer to see how we might be able to control these things. What scares us is there are many other important, pristine rivers and springs in the state that are susceptible to this.”

Bonner and Garrett make this plea to aquarium owners: Don’t throw anything — plants, bugs or fish — from an aquarium into any body of water. “Our efforts to control these fish will do no good if people turn around and put more fish in,” Bonner points out.

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