I know I'm a little late here but the fish in question IS a black tail/columbian shark they ARE brackish and they get VERY big, I know this b/c I made the same mistake.
Fig8 ARE BW no doubt about it, they start out fresh and then go to BW any site that say's they are FW ARE WRONG, I know this also b/c I am looking into getting a puffer tank and have researched them and asked several questions at several forums.
Graphic, I read the post you were talking about (the bala one) and YOU ARE SOOOOOOOOOOO CORRECT!!!!!!!!!!!!!!!