MONSTERQUEST - Piranha Invasion

History Channel - Original Air Date: 3/3/2010

This episode of MQ posits that swarms of vicious piranha may be infesting freshwater rivers and lakes in the US.  Naturally, there are plenty of stories of fishermen catching piranha in the US.  But can a warm-water fish breed here, or are the sightings just pets set free?  Naturally MQ frogman Dale Pearson and company go to Tennessee to check it out.  But piranha don't seem to like the raw chicken being used as bait, and electrical wire dumped in the lake prove more dangerous to the diver than razor-toothed fish.  Of course, the show does feature scary fish stories as well as snatches of history and science.  The scariest stories come from South America, the piranha's native habitat.  There, piranha can pose an actual danger to people, and naturally nets strung to catch them turn a few of the ornery little bastards.  So do fishing lures; the piranha seem attracted by movement through their territory.  A scientist testing piranhas' reactions to cold temperature discovers that they get more sluggish the lower the temperature goes.  Though the fish can survive with temps in the upper fifties, when the water drops below fifty degrees, they're toast.  There are some warm inlets to the lake investigated, but -- despite the show's melodramatic warnings -- it seems unlikely to me that piranha pose any threat in the US.  At least, the show gives no solid evidence of any such threat.