This little jewel of culinary wisdom is too good not to share:
In Eric Ripert's book "Avec Eric", after giving the initial searing, roasting, or grilling instructions, all the fish recipes have the same tip to check the inside of the fish for doneness:
"...finish cooking the fish until a metal skewer can easily be inserted into the thickest part of the fish and, when left there for 5 seconds feels just warm when touched to the lip."
And that's it. Fish-wise, this one simple action is the best thing that's ever happened to me. I'm darn happy with the land-meat skillz and "feel" developed over time, but have had more difficulty with fish that's either undercooked or overcooked, which sucks, because like many of you here we love fresh fish and eat it as much as possible. And with the prices these days, fresh wild caught--or really anything good--is too expensive to ruin even slightly.
It's only now occurred to me that while the countless fish recipes we've tried from cookbooks gave clear instructions for flavoring and technique, none of them told how, exactly, to know when the deepest part of the fish was perfectly done. Some say "cook the fish until done" (uh, thanks?) or give USDA regulations, and I've even stood there like a tool with a digital probe stuck in the side of of a beautiful thick fillet--then overcooked it anyway.
Since the very day we bought the book, with a little stainless steel cocktail toothpick I've used the touch-the-skewer-to-the-lip temp check on a dozen various fish preparations from sauteed, broiled, and roasted, and from the thinnest to the thickest cuts it's been absolutely flawless. Hard to believe that the moistest, tenderest, best tasting and most perfectly cooked fish I've ever had outside of Le Bernardin is from my own humble kitchen--and every single time. Better than most restaurants for sure. In fact, do this with your fish every time and soon you'll be bummed when you order it out how poorly most restaurant fish is cooked.
Give it a shot with your next fine fillets, fellow fishheads!