What are the rules? Serving fish rare.
My understanding is that previously frozen fish can be served still rare in the center. Cookbook authors such as Jacques Pepin suggest serving fish cooked to a lesser degree of doneness, but give no further guidelines. Wild fish versus farmed? Does it have to have been frozen? Only sushi grade? River versus deep water? My cousin likes her fish to 136 degrees, Jean-Georges Vongerichten says salmon is done at 120 degrees. So what are the rules? (Assuming a healthy immune system, and that the fish has been stored properly.)
You are asking a loaded question with many answers. It would be like asking if beef should be served rare, medium rare or well done. Just like everything depends on the cut of beef, everything depends on the type of fish. I would never eat Tuna cooked past rare and I dont think I would ever eat something like monkfish or halibut less than cooked through.
Sea fish is best raw or just seared. You need fish that has been deep frozen to kill any parisites, however. On the other hand, I've been deep sea fishing in various places where I've taken fish out of the water, filleted and sliced them, and had the best sashimi of my life. I guess the pleasure was worth the risk.
All fish tastes better not overcooked. You need to ask others, Google, talk with your fishmonger on a case to case basis. The problem does not seem to be pathogens, but rather parisites.
The FDA says the only fish that can be served raw without first flash-freezing to kill the parasites is tuna. I've caught and cleaned enough salt water fish in my life to know how parasite-infested and worm-infested most fish are. Sushi grade means they cut off the bits with worms. A healthy immune system doesn't help with parasites. If it's not tuna, you really need to cook it through or freeze it first.
Interestingly, on the Toronto board this question was posed when a restaurant served lake trout raw. Here is the response from the restauranteur:
Here is the whole thread: http://www.chowhound.com/topics/42153...
Ok, so I decided to email Globe Bistro to ask about the raw trout and Ed, the owner sent me a timely and professional reply. He told me that in dealing with the freshwater fish tartare, they had long discussions with the farmers and were told the fish are naturally raised fish on farms that are well fed and maintained. The farmers told them that parasites are more of an issue in warm weather and in conditions where the fish have to bottom feed on whatever may be available. The farmers claim there is not a substantial risk but did admit that there is the possibility of parasites and that they could not rule it out entirely.
As a result the restaurant had two options presented to them by the fish supplier: 1) They could "pasteurize" the fish by heating the trout to 175F for at least 3 hours or 2) they could freeze the fish to less than -20C for at least 24 hours.
Ed told me they tried both and found that freezing left the fish texture a little more delicate, but substantially unchanged and that this route was a more practical for the kitchen.
So to make a long story short, Ed indicated they freeze the fish for the tartare before they use it because food safety is paramount.
He also indicated he read my post on CH and was sorry about porkchop and said if I had notified him of the problem he would have taken it off of our bill.
Other than fresh sushi grade tuna from a reliable fish monger, I would not serve any fish less than thoroughly cooked. I would worry way too much about the risks and I don't like the texture or looks of, say, undercooked halibut. I would leave the under-cooking to restaurant professionals as they not only do the research as to what won't kill their customers, they also very likely get better and fresher quality fish than most regular consumers. I might make an exception if I'm buying right off the dock in Hawaii or Cabo, but likely not.