[Dilmah G]

That was probably one of the first tests

It's ALWAYS the first test

If SOC managed to capture Shivan fighters, as we know they did, and if GTVI engineers poked through and upgraded said fighters, as we know they did, it stands to reason that the GTVI is in possession of at least four Shivans, dead or alive.

Unless they believed it inhumane and threw them out into space due to some intervention by a 24th Century version of Amnesty International.

[Blue Lion]

Or if they captured unused fighters

[Dilmah G]

Unused fighters? Wouldn't they have to get inside a fighterbay for that to happen? Since we didn't see any Enter the Dragon-esque depots in FS2.

[Blue Lion]

Doesn't mean they didn't happen.

[NGTM-1R]

Just makes it extremely unlikely.

Even the fighter in Enter the Dragon is actually manned, as are the others at the depot.

[Killer Whale]

They may have blasted beyond recognition or a least beyond usefullness during the taking of the fighters. Or maybe they commit suicide before their capturers can get them.

[Mikes]

It's said several times during the campaign that the Shivans destroy races who use subspace to prevent those races from destroying other, less powerful races.

Like a natural defense mechanism of the universe.

That has been pure speculation of other races who "observed their behavior".
But that "observed effect" may as well be a coincidence and may have nothing to do with "why" the Shivans do what they do.

The mystery is part of their charm

[eliex]

They may have blasted beyond recognition or a least beyond usefullness during the taking of the fighters. Or maybe they commit suicide before their capturers can get them.

If they were manned, by would not have surrendered to the capture team in any case being depicted as a race that doesn't care much for individual losses especially one so insignificant as a pilot of a basic mara.

[NGTM-1R]

They may have blasted beyond recognition or a least beyond usefullness during the taking of the fighters. Or maybe they commit suicide before their capturers can get them.

Doubtful; it takes an awful lot more to destroy a body completely then it does to kill it. Even assuming the Shivans have cybernetically redundant-ified themselves greatly, we still saw one go down long enough to be secured by a sharp capture team in Hallfight (and that's assuming it wasn't actually killed, which we can't really prove one way or the other).

The suicide theory has greater merit, but I think it's noteable that they say "all experimentation on live subjects", not "all experimentation". The Shivans weren't removed from the picture entirely until after GTI was, so it's almost certain that the GTVA has intimate knowledge of their physiology. What they know may not be terribly useful in determining how a live Shivan behaves, but they're probably pretty certain on how to best kill and incapacite them.