Mastacembelus can
      dig under gravel. Here it is looking out the hole.

Macrognatus dag under
      gravel, and you see only its head

Mastacembelus armatus

Mastacembelus frequently digs under gravel so you see only its head. Now it is watching me while I'm taking a snap. It can be entirely in the gravel for a while. My mastacembelus was 35 cm long. This fish length may be up to 50-80 cm! Eats small fish! Not suitable for tanks under 300 l.