Yes very small bread crumbs will be fine, i researched for you just be careful not too big of the pieces of bread, you could even get bread crumbs from the store and break up in the fish bowl but not too much
Is it okay to give goldfish white bread?
I have read and heard that you can give white bread to fish, in very small pieces but some say it may cause the water to turn cloudy. I don't know how true that is so you may want to stick to fish food.