I would say no, unless it was a hardy fish. Your ammo will go back down, then get a fish, or another shrimp, and feed it every couple of days. I bet in a week or so your ammo will have dropped to nothing. Also get another test kit to make sure you are not getting a false positive, or just misreading the test kit. If you don't want to add any livestock, then throw in a pinch of food every once in a while to keep the bacteria population up. Crabs, and even shrimp, don't really contibute much to the bio load, even if you feed them. Fish contribute more because you have to feed them more. And even if they eat every last bit of food, that food get's turned into.....
...."poop",..... which contributes to the bioload, and builds up the bacteria population to the level it could handle a dead fish or critter, without causing a huge ammonia spike. Providing your bio load is not maxed out . Other factors go into also. But now I'm getting confused....