Here is a hint: "This study was undertaken to determine whether this fish could metabolize ammonia from their environment into other, less toxic products......... The data reported here show that this fish can indeed take up and metabolize ammonia."
Sorry, I cannot site the source as that would give it away.
Well you all know me. I have to throw you all off the trail. As you know, I keep no sw fish. So one might think I know nothing at all about the dark side. And you would be mostly right