Indeed.
The default condition for bony fish (everything from birchirs to pufferfish) is to have lungs, unless they've lost them. All the basal bony fishes (i.e., those that lived ~350 million years ago) had lungs. The hypothesis is that bony fish evolved in habitats with an unreliable oxygen level, so needed to use air. Whether this was a brackish or freshwater habitat is still debated, I believe.
As they evolved, some retained the lungs (giving rise to lungfish for example, and from them the ancestors of land vertebrates like ourselves). A few on the "main line" to the teleosts (advanced fishes) kept their lungs, too. The bichirs for one, and also the garpike and the bowfin. In garpike and bowfins the lungs are also used as a bouyancy aid, but remain connected to the 'windpipe'. Eventually, the lung becomes a swim bladder, but in lower teleosts, such as catfish, herring, salmon, etc., it is connected to the windpipe and needs to be pumped-up with air (to some degree or another).
Only advanced fishes have completely isolated the swim bladder from the windpipe, and are able to pump up the swim bladder using only gas secreted from the blood. These are things like perciform fish (cichlids, etc.). Hence, when advanced fishes need to breathe air, they need an alternative to the lung, such as the labyrinth organ.
Paradoxically from our perspective, the lungs we rely on are the primitive condition for bony fishes!
Cheers,
Neale
PS.
cane76 -- Bichirs breathe in through their mouths, and simulaneously the old air goes out the gills. Watch closely and you'll see this happen. They don't "fart" it out. Some fishes do do that, mostly things like catfish and loaches that breathe air by swallowing it and abosrbing the oxygen across the intenstines. So why your birchirs are "farting" is a mystery to me, and it doesn't sound like normal behaviour to me.
bichirs have functioning lungs
a few little bubbles
