How were the Hurrah Conquered by the Creterakians? 

According to "Rise to power:  the Quyth Concordia 2752 to Present" The Hurrah are the only species in the Galaxy who can survive on Gas-Giant planets.  The ability is seemingly similar to the Quyth's ability to live on Irradiated planets which protected them so effectively during the Creterakian takeover of the Galaxy.  Now, Given the Creterakian Stratgey of Bypassing navies to attack planets with Waves of shocktroops, How did the Creterakians take over the Hurrah if Creterakian troops couldn't survive on the Hurrah planets (Note, all Hurrah planets are Gas Giant planets)?  Did the Hurrah, after the collapse of their fleet, Just surrender?