You might be having a hard time finding information on that species because your scientific name is not up to date!! I am at work so I have no referance, but I believe it is Auriglobus Modestus, also known as the Bronze Puffer, Avacaldo Puffer, Bottleneck Puffer, or Emerald Puffer.
If my memory serves correctly, this is a pure FW species. Im sure it would benefit from some Salt content in the water, but it is definately far from brackish. I am unsure how it would react to a higher hardness and pH, but most puffers are very adaptable. Regardless, I would reccomend FW salt as oppose to marine salt.
http://www.pufferlist.com/ Has some good basic info on them. Auriglobus Modestus was correct
They are very active open water swimmers, and I would reccomend eventually upgrading the tank. Give lots of hiding spots and broken lines of sight to keep him entertained and prevent 'glass pacing' in the corners of the tank. Most puffers are very skittish, especially in small tanks. I have a Figure-8 Puffer who has an entire 29g tank to himself, with tons of decor, and still darts around the tank when I walk up to it. Give him more cover, and they will feel more comfortable and less skittish. Basically try to 'overcrowd' his tank with decor to the point where you can barely see the back of the tank.
As far as feeding, once he gets settled in, it should be no problem. Stay away from smaller foods like bloodworms and brine shrimp(messy), and stick to meatier foods like Krill and Silversides. Giving him ghost shrimp, will not only be entertaining for him, but for you too. I would even attempt to give him some small FW crabs (declawed) when he gets used to feeding regularly. When he gets hungry, he WILL eat.. You might have to put the shrimp or krill on a chopstick and dangle it in his face though. I enjoy using freeze-dried krill for my puffers because its crunchy and it floats.
and YES, it does matter if its brackish or not. Ignorance like this has killed thousands of puffers, and even though they can endure brackish conditions for a short time, long-term health is the major issue here. There are only 3 or 4 species that belong in true brackish water (marine salt, not FW salt), which would be T. Nigroviridis, T. Fluviatilis, and T. Bioccelotus(GSPs/F8s), the other few species that are brackish are very uncommon in the aquarium trade.. (Fugus, Juvie Marine puffers, etc.. You would know, as the price would reflect its rarity)..
Hope that helps, and good luck!
