Monster catfish and its creepy smile invade PA rivers

These aquatic apex predators can reach up to 100 pounds. Breakthroughs, discoveries, and DIY tips sent every weekday. Flathead catfish () may look like they are perpetually smiling, but these five foot-long fish are no laughing matter in regions where they do not belong . The opportunistic predators are now one of the top predators in Pennsylvania's Susquehanna River, creating a major threat to the local food web. Without any natural predators to keep them in check, these enormous fish can alter a river system in only a matter of years.