Yes, have vegetables prepared. Squash slices, cucumber & zucchini slices. If you don't like to heat them, just tie them to a rock or driftwood. They may not eat it immediately. Try not feeding them for a day or two then introduce the vegetables. Just keep trying.
You can also give them frozen bloodworms. These they will most likely eat. These are, by far, the most to nature that they may get aside from algae. I am so sure that these fish really dig or go for those little slugs at the bottom of the river, lake or pond. Clam and shrimp bits will be relished but, as in some of my tanks, they do leave leftovers.