Colorful aquarium fish have invaded Waller Creek.

The creek’s population of platy fish, native to northern Mexico, has reached the thousands according to research done by environmental science senior Han Ooi. 

Adam Cohen, a UT ichthyology collection manager, said many students keep these colorful fish as pets because they are relatively easy to take care of, but these students often try to find ways to get rid of them at the end of the semester.

“After the semester changes or the summer starts, most students wonder what they are going to do with their fish,” Cohen said. “The creek is right there, so they drop them in there. Most of the time the fish die, but every once in a while, this happens.”

Biology freshman Elizabeth Clark said she is familiar with what it takes to raise a fish. Clark’s sixth-grade science project turned into a small ecosystem of over a hundred live-breeding fish at home. She said she took none of them to UT because she expected it to be hard to take care of them while in college. 

“It’s nice to have something to care for,” Clark said. “It can really distress you at times, but you have to think of how stressful it is on the fish to be moved between home and dorm. People really don’t know what they are getting into when they get a fish.”

Ooi is studying the platy fish population in Waller Creek as part of his capstone research project. He said normally this species would not be able to survive the cold winters, but the urban environment creates optimal conditions in the winter. 

“My hypothesis is that there are warm water outflows from pipes,” Ooi said. “These waters are creating warm thermal refuges for the fish during winter. That is why they are able to survive.”

Ooi said research has not yet determined how the platy fish invasion has impacted the native environment. He said the platy fish would be very difficult to get rid of if they are found to be harmful to the environment, like many of the other invasive species in the creek. 

“Almost half of the things I’ve seen in Waller Creek are nonnatives,” Ooi said. “Waller creek is kind of a dump for everyone. People throw what they don’t want in there, including plants and animals. It is kind of a mixture of everything.”