Incredibly fussy eaters. I have one and the only prepared food it will consider is mysis. If yours won't even touch brine shrimp then you definitely have an uphill battle ahead of you, good luck.
Maybe try some live oysters or live clams from the grocery store (someplace like T&T if your local Safeway or whatever doesn't carry that). Crack the shell open and plop it in the tank and see if he'll at least eat that.
Course, if he comes to expect that then there may not be a lot of incentive to try the mysis, but it may at least get you over the initial period.
There is also clam juice at the grocery store that you can try soaking food in. Now, mind you, I tried it, to get mine to try pellets or flake, and it didn't work. But it might work for you, it's worth a shot. BTW, it's putridly vile stuff, I have no idea how to tell if it's gone bad.
