exactly.
What Silurus doesn't mention, but he hints at:
fish do not have a nostril wich is connected to the roof of the mouth or the back of the throat....they cannot "breathe" by entering water (or air) through the nose.
There are a few exceptions: lungfish, and the now extinct fish like Eusthenopteron wich are on the root of the evolutionary tree of all landdwelling vertebrates.
the nostril wich connects the outside to the inside of the mouth was an invention by fish aiming for life on land, so to speak
the other "tribe" of fish (all the other fishes from herring to swordfish) use their nostrils only for sense of smell and thus the nostrils are some sort of "U" shape (or tunnel) wich has entrance and exit; both outside.