just keep trying. My plecs sometimes take weeks to realize that a zuccini is food. Also, don't look in the tank and bother the fish. If it starts to associate zuccini with a big scary person looking in on him, you're sunk.
drop in the zuccini (raw, only blanch for tiny fry) in the tank, turn out the lights, and leave the fish alone until morning. keep this up until he eats it. it's really as easy as that.
drop in the zuccini (raw, only blanch for tiny fry) in the tank, turn out the lights, and leave the fish alone until morning. keep this up until he eats it. it's really as easy as that.