Some species are confined to acidic black rainforest waters, and others are found in clearer, neutral to somewhat alkaline waters; a few species are even adapted to both kinds of waters. However, there are no brackish water species.
Certain species are limited to the acidic and black conditions of rainforest waters, whereas others can be found in more balanced, neutral to slightly alkaline waters. Some species have adapted to survive in both kinds of aquatic environments. Nevertheless, there is no evidence of species that can tolerate brackish water.