I found mine would eat anything. Lettice dissapeared, shelled peas. They used to eat algae wafers like biscuits (cookies). They used to try and eat the cucumber but couldn't really get it in their mouths. Oh and any plants I put in they'd destroy
no iceberg lettuce, it has about as much nutritional value as water, try romain instead.
also i used to give my big redhook walnuts every so often, not good as an every day thing but fine every few weeks or so