Yes shell the peas. Cooking them will cause a loss in nutritional value and end up messier on the tank, though blanching them (a very quick boil) will help them sink and be more easily consumed.
most larger fish , say over 4" will have no problem eating the whole pea skin and all , smaller fish should have the skin removed and maybe quish the pea a bit to soften it .
I esp agree with freddy on cooking , or none cooking .
