While Hexanematichthys seemanni has a high tolerance for freshwater physiologically, when kept in a freshwater tank all they do is swim frenetically trying to "go downstream" into the estuary. These are estuarine fish, and expect to be in brackish water, end of story. They are also schooling fish, and they are very, very unhappy kept alone. Adding a couple more to your collection will make all the difference. Despite their reputation as predators (which they are) unlike most predatory catfish, these are sensitive, shy animals that really need company of their own kind.
Cheers, Neale
