All other fish accounted for? Any inverts in the tank, like snails? Dead snails can foul a tank pretty quickly. This is the "chicken or the egg" scenerio. Did you remove the wrasse right after it died? IF so it is more likely that NH3
killed the wrasse instead of the dead fish producing NH3
But you added a Picasso Trigger to a 55 reef and wonder where the ammonia spike came from.
While a 55gal is certainly too small for a trigger I doubt the simple addition of the fish would cause an NH3