Yasha goby question

[thesaiyans]

So my husband and I have a yasha goby that feeds from an eye dropper and swims out in the open comfortably within our 10 gal AIO LPS tank. As my husband was watching him he noticed his mouth open really wide and a big round like bottom to his mouth that looked like a whale when they extend it. Does anyone have a photo of this by chance and possibly know why it did this when it wasn't feeding.

 

[i cant think]

So my husband and I have a yasha goby that feeds from an eye dropper and swims out in the open comfortably within our 10 gal AIO LPS tank. As my husband was watching him he noticed his mouth open really wide and a big round like bottom to his mouth that looked like a whale when they extend it. Does anyone have a photo of this by chance and possibly know why it did this when it wasn't feeding.

One thing I can think of as to why is aggression and showing dominance, although in the two years of owning mine I have never seen it do that (Although, it has been with 4 other peaceful fish that never bother it)

 

[jrill]

A couple of my gobies do that when chasing things away from their hole and shrimp