I've hatched a number of these sharks in the stores I've worked in and have found 2 foods that usually work great. (First off, look at the shark's belly. If you see red in it, you don't have enough oxygen in the water to support the shark so you will need to address that first before you will get him to eat.)
The 2 foods are fresh clams and bait squid. I went to the local fish market and got live cherrystone or little neck clams and slit one open and made sure I cut into the "meat" of the clam then put the half shell in front of the shark so that he could smell the food and go to it itself. Squid: go to the local bait and tackle store and get a small pack of bait squid. You will need to clean it out but keep the tentacles. Cut the body into thin strips and then cut the strips into approx 1" pieces. These pieces should appear to flutter in the water which should attract the shark to eat it as well. Use tongs or a stick or something to bring the squid strip close to the shark's face so that your finger doesn't scare the shark. Once you get the shark eating, you can also feed the tentacles. ( You can freeze the squid after you cut it into strips.) For starters, you shouldn't try to feed the shark a lot of food. 1 or 2 pieces should do it for the first time. Once it starts eating, you can up the amount at each feeding.
But check the belly first.
Hope this helps.