I give my cats the occasional shrimp from the freezer (usually pre-cooked), but I don't think they should be fed regularly because that would be the same as feeding fish except possibly even worse. They are fattier than fish, but not the good kind of fat since they are bottom dwellers (feed on other animals waste). I imagine their salt content is at least comparable to fish, and eating too much seafood creates a buildup of mercury that cannot be expelled from the body. I've never researched it, but I assume that cats can get mercury poisoning just like people if they eat too much seafood.
Every Friday Mow and I eat cooked Dunganess crab. He's never had any bad reaction to it in almost three years of eating it.. He's been offered shrimp but rarely eats it. He likes Cod and has eaten lobster with no reactions. I always buy wild caught for me, so that's what he gets on the occasions he gets it. He'll only eat fish cooked, I've offered but he turns it down if it's raw