Help me out here, 
If thought of as **electron sea**, there's is no need of holes in modeling **conductivity in metals**. But it's not that we can deny that there will be positive charge in the nucleus after electron goes in conduction, however small its effect is. ( the effect would be small enough without small interaction electron would never had got easily detached from individual atom) 
The metallic bonds are some kind of covalent bond more inclusive then covalent bonds in semiconductor which occurs between only neighboring nuclei, there should be a **generation of holes**. And cause there is a sea of electron in conduction band, there should also be a **sea of holes** in valence band which can or cannot contribute in conduction (that's specifically i want to know) .
Can you add something into this..

**arguments maybe not structured so please ask right away**