firefish - diamond goby pair

[EPRuss]

Just curious how common this behavior is:

I have a firefish and diamond goby that seem to have some sort of relationship. They both share the diamond goby's burrow. During the day the firefish hangs out in the burrow (he comes out for a few hours around feeding times), while the diamond goby moves around the tank sifting sand. At night they both enter the burrow and the diamond goby closes the entrance by piling sand in front of it. The diamond goby also protects the burrow entrance from snails throughout the day. If a snail gets to close to the burrow entrance he will pick it up and move it somewhere else.
This behavior has been occurring pretty much sense day one of the two fish being together in the tank (about 6 or 8 months now). I mentioned it to my LFS and he was very surprised. So I was just curious if others have observed similar behavior with these two fish, it seems that they are both very common fish to house together.

 

[eatbreakfast]

Dartfish will use whatever burrows are available to them. I have had pink bar gobies and blue gudgeons use a jawfish burrow, and firefish go into the burrow of a pistol shrimp and watchman. In the wild and in captivity they use other fishes burrows as "bolt holes" all the time.

 

[EPRuss]

So more like a freeloader than a partner?

 

[snorvich]

So more like a freeloader than a partner?

Exactly.