Get him some fresh clams, chopped and fed on the 1/2 shell. I’m pretty sure that it will eat the shell too?
Most importantly; have a straight talk with your fish. Tell it that you rescued it from the people at the lfs who pulled it out of the sea. You plan on providing an ever home and you hope that your fish will forgive the people that pulled it from the wild.
Let the fish know that you are not planning on eating it for dinner, but are only concerned for it’s well being and comfort. Also, it’s in qt, but the DT is much bigger and it will have other fish to be with once it has been treated for parasites, cavities, and bloating issues should they occur. Tell the fish that you love it and plan on feeding it good food going forward.
The fish will listen and if you follow through it will learn to trust you and relax in the new home, unless it is unable to adapt to fish tank life, but let it know that is not a good option, please thrive.
I have never had a fish not thrive once it decided too. Talk about it today. If the fish spits water after you are done, then feed it and remember; It’s a puffer. It may want a smoke?