Spotting frozen seafood in restaurants We've just been to Spain and while we were there we ended up in quite a touristy restaurant. There we ate paella which was terrible, at least in my opinion. Then I was wondering how fresh (or not) it was. The prawns were still in their shell but some of them had developed some white areas.

So my question is: do these white spots on the shell indicate that they had been frozen? Or can a prawn go white too if it is boiled or fried straight after being caught?

Just for the record: I'm sure they had been frozen because they didn't taste very nice.
As Rumtscho said in her comment, much seafood is frozen on the boat before it even gets ashore, let alone into a restaurant. However, it is possible to keep seafood fresh using another method. Good seafood restaurants will have live food in tanks ready for eating. I often go to such restaurants and pick out my fish or crab from a tank and watch as the waiter nets it out. In my local market I can buy shrimp still jumping about in the bag as I carry them home. If you insist on fresh seafood, then look for places like these. Usually they will make a show of the live fish in tanks at the front of shop/restaurant.

To answer your question: If you don't see it jumping about live before it's cooked then assume it's either frozen then cooked, or cooked then frozen, or maybe cooked then frozen then cooked again.