Based on my limited experience, try to condition them to feed on the surface. I used cabbage to start, then almost any veggies that floats after that. Once they learn to eat anything on the surface use whatever you are tossing in at the time. The reason I used floating stuff was that I wanted to see that it was being eaten and not just rot on the bottom.
But, mine were conditioned to pellets first.
The other thing that works is a flavored bread/dough mix same as carp fishing, use either a bobber of fish the bottom. Here strawberry flavor is good.
There are other links here do a little searching and you will probably find what some one in your heighborhood is using.
