Other somewhat arowana-like fish:
You could go with dragon/ violet gobies in a brackish setup. They typically get to about 15".
http://www.thefishworld.co.uk/id184.htm
Smaller bichirs such as Erpetoichthys calabricus, Polypterus senegalus, P. palmas, and P. delhezi would also do well in that tank (they are strictly freshwater species, not brackish); the Polypterus I mentioned reach about a foot in length, the Erpetoichthys is longer but slim and eel-like. They have a whole section in the Ancient Fishes subforum; just read through the stickies down there.
You could go with dragon/ violet gobies in a brackish setup. They typically get to about 15".
http://www.thefishworld.co.uk/id184.htm
Smaller bichirs such as Erpetoichthys calabricus, Polypterus senegalus, P. palmas, and P. delhezi would also do well in that tank (they are strictly freshwater species, not brackish); the Polypterus I mentioned reach about a foot in length, the Erpetoichthys is longer but slim and eel-like. They have a whole section in the Ancient Fishes subforum; just read through the stickies down there.