I am not entering this as an argument, but rather as some references that I keep which state brackish keeping.
1. Aqualog Special #12 Brackish-Water Fishes (Frank Schafer)
Aqualog Special #12 states that D. microlepis and D. undecimradiatus are completely freshwater fishes. Inversly, Schafer lists D. campbelli and D. quadrifasciatus (Schafer includes both fishes from India and south-east Asia as D. quadrifaciatus as they continue to work out the taxonomy).
Geography - D. microlepis Sunda Islands & south-east Asian mainlands
- D. undecimradiatus Cental & lower basin of the Mekong
- D. campbelli New Guinea but does travel up the Fly River for short- term maintenance
- D. quadrifaciatus see above
2. Encyclopedia of Aquarium & Pond Fish (David Alderton)
Alderton list D. microlepis are brackish (SG 1.002-1.007)
3. Brackish-Water Fishes: An Aquarists Guide to Identification, Care & Husbandry (Neale Monks, Editor)
Dr. Monks, along with other colleagues, penned this guide. Here Datnoides are listed as adaptable euryhaline fish, meaning tolerant of a wide range of salinities. It suggested that D. microlepis, D. campbelli & D. quadrifaciatus be kept at SG 1.005-1.010 (leaving others to freshwater). Although tigerfish can be adapted to a freshwater aquarium, their long-term health is best served by adding at least some salt to the water. Lower range keeping is advised around SG 1.003-1.005.