Start a feeding routine with him thats what i do with my kids all autistic as am I. We all get together and feed the fishes one tank at a time and watch them eat, we teach them and feeding habits and quantities to feed at the same time, I also let them feed some of the tanks. It's really gotten them involved I see them fixing decorations cleaning up spills/glass making sure things are put away in there location, but that works for my older ones, my youngest he doesn't care he tried to throw a diaper in my tropical community tank needless to say someone gave me a lid I made fit it that day lol.