I know there are peacock bass on a few of the islands.
Kaui and Maui I think...Lake Wilson is one of the places. NOt sure what island...maybe Maui.
I think Gulf Killifish may be found in brackish water or in Pearl Harbour.
You catch any snakeheads yet? They are on Oahu. There's some Hawaiian red shrimp too and some unique freshwater snails.
They still raise them for food in ponds on the north shore, you can purchase them in Honolulu's China town. They're still live but they won't sell them to you until they kill them.
Not sure if Dr. Cray has seen this forum yet but it has a lot of good info on Lake Wilson - http://www.hawaiibassfishing.com/
EDIT: Nevermind, I see he's posted in the forum over there.