Wendy Gomersall mentions a number of fun parts of traveling to Laos and glosses over the rumor of the Man-Eating Catfish, but it's still worth reading at the Daily Mail. It basically boils down to "Mekong giant catfish (at 10.5ft long and weighing about 660lb, this is world’s largest freshwater fish. It’s supposed to be largely vegetarian, but local people aren’t so sure)."
Tsk. Giving away the best part of the adventure. But as a hint, especially as we enter October, giant catfish would be the least of your problems if something really wanted to eat you out there.