Habitat: Goby: from Bali to Japan; Shrimp: Marquesas Islands and parts of the Indian Ocean, including the Seychelles
Status: Not Listed
Here’s one of the coolest odd couples you’ll get to see for quite some time (unless you live in Los Angeles, in which case all you have to do is walk outside for an instant freak show). This is the Magnificent Sailfin Goby (Flabellogobius sp.) which has recently been making the rounds at various aquarium trade shows. These guys are kept with Red-banded Pistol Shrimp (Alpheus randalli) because they form a special symbiotic relationship with one another. 

Much like other goby species, these fish become “best friends” with burrowing shrimp to create a unique partnership. The shrimp maintains a burrow for the pair, cleaning out debris and making it a safe place to come home to. The goby, meanwhile, acts as the watchman for the two creatures by alerting the poor-sighted shrimp to any potential danger by darting back into the burrow with the shrimp following close behind. The goby and shrimp keep in almost constant contact with each other, the shrimp using its antennae, and the goby flicking the shrimp with its tail when alarmed. 
Basically these two both get something out of their friendship: the shrimp gets protection and the goby gets a clean house and a safe place to lay its eggs. That’s more than I get from some of my so called ‘friends.’
Check out the video of this pair in action: