ok, this may sound sick.. but what the hell, give it a try..
I got mine a while back, they were in terrible shape and I mean terrible.. they were really starving, they didn't get the shrimp thing, much less the pellet thing but they followed my finger with some interest because it moved.. what I did was I triggered them to shoot at the glass and snap, the idea light bulb came up.. i dropped pellets and shrimp just in front of the front glass and did what you can do with a cat and a laser pointer and damn if they didn't eat.. I fooled them in to shooting at my finger through the glass, only problem was there were shrimp and pellets in the way..
anyways, this isn't the regular method and if that means I'm the dat-wisperer or a complete psyco is up to you, all I'm saying is it just might work..