If it only eats live, a spearer needs fish.
I feed them whatever the rest of the fish was eating that night. If it's a clubber you can stuff frozen food into snail/hermit shells to keep his pummels "conditioned".
I had thee pickiest ciliata. If he didn't "like" it, he would toss it. AND would keep doing so until I offered him something he wanted. So, thinking he didn't like the rest but preferred the last feeds food.... nope. He would toss it and wait for the selections offered the previous feeding that he had tossed. I wish he could read... I would have given him a menu.