I have both. It's kind of an interesting scenario. I had the yellow watchman first and bought the pearly jawfish later. The yellow watchman found little caves to hide in until the jawfish came into the aquarium. Now, the jawfish will build a cave and, within a day, the watchman goby will move into it. The jawfish won't leave for a day or two and both will share the jawfish's little cave. Ultimately, the jawfish will get tired of sharing his den and will go elsewhere and make a new one, but, the goby finds him and moves in with him. I have little holes and caves all around my take and they move every couple of days, following that same process. In my experience, they aren't dangerous to each other, but the watchman goby is an annoyance to the jawfish.
