Born in freshwater, but move into brackish estuaries as they mature.. GSP are high-end brackish fish that are better kept in saltwater in captivity. Its a common myth that if they move around in varying salinity levels in the wild, then its ok to do the same in captivity. The fact is that we cannot simulate this part in captivity without ruining the biological filtration at some point. Stability of the water (and clean) = increased longevity of the puffer life.