My tilapia buttikoferi will position himself in front of my RTC, then turn on his side, the RTC will swim forward, put his head under my tilapia and push him upward in the water, the tilapia floats back down, then repositions himself in front of the RTC. They usually do it 4 to 6 times in a row, untill the RTC gets bored and swims off.
This reminds me that I really need to get it on camera
Edit: I forgot the other thing my tilapia does, hes scared of the surface of the water for some reason. When i put floating food in he stares at it for a while, then will go towards it several times but keep backing down, when he finally takes it, he trys to carefully grab it with the tips of his lips, swim it down, then swallow it. If he misjudges and grabs at the food to fast, it makes a load slap noise, which scares him and he hides.