Twice a year, dozens of spearfishers come to the San Marcos River to participate in a tournament targeting the suckermouth armored catfish. The invasive species took to these waters, as well as the Comal River, when aquarium owners started dumping catfish that had grown too large for the tanks. Spearfishing is the most effective way to remove these invaders. But other outsiders have also made their way to Texas’s lakes, rivers, and oceans. Here are five of the worst offenders. Bighead Carp Native habitat: China How it got here: Escapes from fish farms Why it’s a threat: It eats lots of plankton. Where to hunt: Bexar, Jones, and Taylor counties in the Upper San Antonio and Brazos river drainages; San Jacinto River; Braunig, Fort Phantom Hill,…