I have a fahaka puffer (which is freshwater) but when I first got him he did not eat for a week and 1/2. I put snails, shrimp, and other foods on his "diet" in front of him and he would never eat. Now he is doing great and eating all kinds and often. I think it took him a while to adjust to a new environment and to get used to everything. I know your is SW
and mine is FW
but yours might be going through the same thing. I would give it 2-4 days before I started to worry if I was you. Mine survived for over a week before he started eating.