These pics are better than the pics from your other thread and yes I would say for sure now thats a Green Spotted Puffer. A little young to be in full saltwater conditions already but he should be fine. Judging by his size, he is under a year old and should be in brackish water still. They generally do not leave estuaries until they are adults. Many do not ever leave for the ocean. My brother is a marine biologist and recently has been working a lot with brackish fish and said he has yet to see one venture out to the ocean. He is finding them in water with a specific gravity of 1.010-1.020 or so. But they have been found in the ocean in the past. I think it depends a lot on where the best food source is. They always come back to the rivers to mate though.
Make sure he eats a lot of meaty foods and especially shelled foods. They can get overgrown teeth very easily. Feed lots of clams, mussels, prawns, squid, brine, mysis, ect.
They can also be very aggressive little fish although I have yet to own one that is. I find they are usually ok with most tankmates.
Good luck!
