You should NOT attempt to feed your fish bread regardless of what they are. Bread can swell and as it is also made mostly of starch, I would not be surprised if the fish starts getting bloating issues and eventually buoyancy issues.
I feed my fish boiled egg whites, and gel foods containing veggies, sardines/tuna/mackerel, acidophilus, calcium, multivitamins and Mazuri gel powder. About the only human foods I give them at the moment aside from shrimps excluding Mazuri which is obviously for fish.