Hi, Do you mean a Hexanematichthys seemanni?
If so these fish are a brackish fish that require a large tank. Most of these reach 12-14" but can reach a potential 2ft in length.
A couple of the websites I found suggested a minimum tank size of 400L but personally I reckon you'd need a 6ft x 2ft x 2ft tank minimum for these fish when they reach adult size.
As young these fish can be raised in freshwater but require small amounts of salt adding to the tank as they grow, right upto adult size when they require a 100% marine tank.
Have a search on google for the scientific name I gave you, you'll find much more info there.
Andy