rock/gravel/sand eating fish?

[zoo_edu]

My brother has a fish in his tank that keeps his gravel, etc clean. He doesn't know what it is called and I have been unable to locate it as I have minimal information on it. Anyone ever heard of a fish that does this?

 

[renogaw]

certain gobies, jawfish etc will sift the sand and eat micro organisms out of it. they dont really eat the substrate, just whats in it.

 

[cam78]

Diamond Goby