At this stage i would throw in a few healthy baby guppies... he needs something to eat when he is this young..once you settle him in then try all the other foods you have talked about.. but i like to see them get a little bigger and healthier before they fast like this.. so one more try with the frozen blood worms..{frozen because they are more life like.} shoot with eye dropper in his face...} but then go get the baby guppies if it doesn't work..because you do not want to mess around at 3.5 inches.. thats a little baby... Also make sure you seal up the top.. even the tiniest opening can be a pass for the arowana to end up on the floor.. they are jumpers..