It is common practice to use primary and secondary fermentation. A single primary fermentation will produce mead. However, some choose to use secondaries for clarification and or the addition of fruit to flavor their brews. In order to provide the yeast with essential oxygen to ferment the honey it is best to oxygenate it by injecting oxygen into the must.
Just to clarify, oxyegen is added to must only before or at very beginning of fermentation . Oxidation of partially finished fermentations usually do bad things to flavor and drinkability of beverage. Not that I know diddley about mead, but holds true for beer, cider and wine.