Why do the African Knife breathe air?

[Snytbaggen]

I finally got an African Knife (Xenomystrus Nigri) a few weeks ago after almost a year of searching, so I'm happy. Everything's going fine, it eats well, is less and less shy and it gets along with its tankmates just fine. I did notice that it sometimes darts up to the surface to grab some air, so I started to do some more research since I couldn't remember reading about that. I've found several places saying that it needs to get up and gulp some air every now and then, but not a single place that specified why. Is it because of some swim bladder function? Does it have a primitive lung like bichirs? Some other reason?

 

[Aweshade9]

Yeah it has a primitive lung just like bichirs. All fish in the ancient fish section breathe air including knife fish.

 

[krichardson]

I've wondered about this when Ive seen my afer come up for a gulp.

 

[Tramonte172]

I believe the ability to breathe air is an adaptaptaion that allows them to survive in water containing low amounts of oxygen, where most other fish can not. This is useful during long periods dry weather.

 

[krichardson]

^Makes sense to me.