What?!? If his fish died it wasn't because of the nightcrawlers...
Mine would spit them back out the first few times I fed them nightcrawlers. It's just a different flavor and sensation. Try a few more times and they will eat them.
Last weekend I caught some crawdads and threw them into the PBass. At first they'd suck them in but spat them back out immediately. After doing this a dozen times or so they started fighting over them and eventually ate them all. PBass adapt pretty fast and if it's edible (and sometimes even if it isn't) they will eventually eat what you feed them.