my red survived and grew big only on morio and mealworms, earthworms, bloodworms and bugs. He only ate insects for over a year.
Maybugs are a big favorite but you cannot buy those, you have to catch them yourself.
If you want to induce a crazy feeding frenzy, feed the mealworms some white bread and store them at a litlle over roomtemp for some weeks.(f.e.in the hood of your tank)
The mealworms will turn into black beetles and i assure you the O will love those very much. Plus they don't jump.
On other option may be crickets or grasshoppers, but they will jump and escape.
Or if they do not get eaten right away, they will swim off and then hide in the hood, preparing to hide underneath your tank and driving you crazy with the constant chirping... :angry:
I heard some folks do extract the hind legs, to keep them from jumping, but I'm not the kinda guy who enjoys that, so i never feed crickets anymore.
I was so glad my red finally started to eat pellets, that i didn't dare to feed worms anymore, for i was affraid he'd go off the pellets again.