Yup, the polar bear's liver has toxic levels of vitamin A.
And the fish is the blowfish or, more accurately, the pufferfish. It's fugu in Japanese, and it's apparently easy to get the fish flesh poisoned, so the fugu chef has intensive training to keep that from happening.
I dunno. After experiences with buffets, I'm not feeling lucky, food-wise, enough to try it. If I'm going to risk my life, I'd rather it be through my own actions.
And my memory of the poison fish from entertainment media is an episode of the Simpsons. I don't remember it all that much, but apparently Homer didn't die.