Underwater missions?

[Shadow Archon]

Wrong.

Some Zerg can survive in a vacuum. Zerglings, for one, can not however.

Do you have proof?

The Zerg are composed of several different types of creatures that have been integrated into the Swarm by the Overmind. These creatures, or breeds, have been selectively evolved to become efficient killers and to assist the Zerg in their quest for ultimate power. The Zerg do not utilize technology in the common sense, but their natural weaponry and armor is comparable to the most advanced gadgetry employed by any other species. This biological evolution, combined with an unmatched savagery and their blind devotion to the Overmind, make the Zerg an extremely formidable and deadly foe.

The Zerg have been found in all types of environments, including deep space. They have adapted themselves to the rigors of space travel, although it is not exactly understood how they are able to do so. The center of a Zerg habitation is the Hatchery. Their nests are composed of a thick organic matter, nicknamed the Creep, which provides nourishment for the Zerg and provides organic mass for Zerg Larvae and Drones to facilitate their transformation into larger forms. The Creep expands and covers the area around the Zerg hive, and is very difficult to eradicate.

Because mine says otherwise.

[DemolitionSquid]

Because mine says otherwise.

Each Zerg breed is evolved from an former animal species. Do you think Zz'gashi Dune Runners or Slothen could survive in a vacuum? No. Lesser Zerg eat creep. Lesser Zerg breathe air.

Some Zerg have the ability to travel in space, because they started off that way. Mantis Screamers were traveling the stars long before they became Mutalisks.

[Shadow Archon]

Each Zerg breed is evolved from an former animal species. Do you think Zz'gashi Dune Runners or Slothen could survive in a vacuum? No. Lesser Zerg eat creep. Lesser Zerg breathe air.

Provide proof.

Some Zerg have the ability to travel in space, because they started off that way. Mantis Screamers were traveling the stars long before they became Mutalisks.

The Zerg change each of their breeds in order for them to survive space travel. That would include not requiring to breath. The Zerg got it from Behemoths or the Mantis Screamers though.

As the swarms continued to grow and
strengthen, the Overmind turned its thoughts
towards its own future. It realised that within
a few short centuries its race had assimilated
all of the indigenous life upon Zerus. It knew
that to further evolve the swarm, the Zerg
would need to leave Zerus. The Overmind
began to reach out with its senses, looking
for something - anything - which would
provide them with transport from this world.
That opportunity soon arrived. A race of
gargantuan, space-faring life forms passed
through the Zerus system, and the Overmind
called to them. Drawn to the barren world
by this beacon, they were quickly assimilated
by the swarm. The inclusion of super-dense
hides and the ability to exist in a vacuum
bolstered the genetic pool of the swarm. Soon
the Zerg warriors were conditioned to survive
the harshness of space.

That would include the need to breath, unless you have a source that says otherwise.