The tail of the fish.
You can only just make out the engraving in this photo, and that's after I have lowered the brightness and upped the contrast in PhotoShop.
The eyes and gills.
Dreamtime stories typically describe ancestral totemic animals creating the landscape or establishing some rule of how you should live your life. The stories coalesce to form songlines, which act as oral maps, passed on to all those who have an association with the land. The songlines allow a nomadic people with no written tradition to pass on information about routes and how to survive along the way.