There's multiple possibilities, depends on context. Have a C. gibberosa 'Kapampa' male, when he used to be in a tank in the living room he'd play a game where he'd capture a bubble at the surface, go to the bottom and release it with an audible pop, sometimes he seemed to want to be fed, other times merely amusing himself.
You can find a lot of literature on fish 'vocalization' if you search on "soniferous" fish, including a number of interesting recordings. Sometimes it's related to "agonistic" (combative behavior), sometimes mating, etc.
Here's a link-- you can click on the "Sample" links in the article to hear recordings of soniferous fish.
Here's another link, fish keeping people up at night.
You can find a lot of literature on fish 'vocalization' if you search on "soniferous" fish, including a number of interesting recordings. Sometimes it's related to "agonistic" (combative behavior), sometimes mating, etc.
Here's a link-- you can click on the "Sample" links in the article to hear recordings of soniferous fish.
Here's another link, fish keeping people up at night.