As some of you know, I got my jack dempsey last summer (june or july I think). When I first got it, it would swim all over, eat anything (and from the top), etc. But then after it hit about 5 - 6 inches it hid almost 24 - 7. It wouldnt eat anything except flakes, and would only eat them from the tank floor, or floating in the water. Over the last few days, the fish has changed dramatically. It swims all over, eats from the top again, doesnt seem to like its tank mates as much anymore (the blue gourami is going to be moved, the dempsey doesnt bite it, but it chases and Im afraid biting will be next). It has flared at the pleco a few times and turns alot darker when it gets "mad", it also bit the pleco once when the pleco was moving on it (I wouldnt want to get moved on either, but I hope the biting doesnt continue). Ive also noticed it grabbing plastic plants in its mouth and shoving them around, today it grabbed one and rammed it into the side of the tank. Im glad its starting to act like a normal jack dempsey, although now I will have to be careful about what fish I put it with it. Its about 6.5 inches (maybe a tad less) now. 
. Oh boy