Cooking fish to the right doneness is essential. We don't want to time travel back to childhood memories of gray, dry, tasteless, chewy salmon served at a buffet. Unlike meat, which has different desired doneness like rare and medium-rare - some people claim there's also a thing called well-done - fish only has one level of doneness: The perfect one. It's 125°F. It's when the fish gets flaky on the outside while still firm (pink, in the case of salmon) on the inside.