Funny... I just heard about this bastard on a science podcast a few days ago.
Yeah, surgery or *gulp* amputation is the best solution cuz you can die from this pretty quickly, as you might imagine.
But apparently, if it isn't immediately life-threathening, a shitload of vitamin C can soften the spines so you can piss it out. More about it here... http://www.bbc.co.uk/dna/h2g2/A35669460
Also, this would be more for if the fish was lodged in the peehole (a term I prefer), rather than something that was actually supposed to travel up into the bladder. Damn, I wish I could remember where I read it.
It really should have been a fat college kid on mushrooms or something. It doesn't make sense that a guy who grew up the river would let candirus into his bladder all willy nilly.