Bangai cardinal issue

[Don's tank]

So it looks like there's something popping out of its gills. Almost like a bladder is overinflated. Hopefully the picture is clear enough to see what I'm talkin about. Please let me know if you have any suggestions

 

[Auquanut]

Kinda hard to tell from the picture. Do you have 2? It's possible he could be expecting.

 

[Don's tank]

I tried to improve the picture a little. The only other cardinal I have is a pajama cardinal and I assume they don't cross bred.