Most of the Ackabar sources are metioned in Later SW books, or in the RPG.
from WEG SW Source book:
The first calamari starship met the Empire, and made peacful overtures. The Empire, however, didn't see an advanced cicilization with which to trade; it saw instead an advanced technology and gentle, and therefore stupid, fol ripe for conquest. The Empire saw a natural slave species whose industries could be exploited to serve the Empir's war machine.
When the Imperial forces invaded, they were welcomed as freinds. But when the Empire began seizing proerty and treating the instuments of Calamari power and governace with contempt, a few were moved to passive resistance. The Calamari were enslaved, but they would not easily give up thier freedom.
The Emperor would not stand for any definace. He ordered the destruction of three Calamari cities as an example of his power. The sea swelled with the blood of thousands. That, he was sure, would cow his foes.
The response was unexpected. This peaceful species, this world with no history of war, rose as one turning the utensils of peace -- kitchen devices, gardening implimants, metal working tools -- into weapons of war. The Calamari destroyed their enimies, throwing back the first wave of invasion.
The Emporer tried to make slaves of the Calamari; instead he taught them war.
As far as i know there is no EU information concerning his life before he was a salve, except for him going back to his roots in the Jedi Academy Trilogy.
Ackbar was rescued when tarkin was enroute to the Death star. Rebel special forces planned an Assassination on the Moff, but due to the interferance of a ISD (which resuced Moff) Ackbar was left behind, and later joined the Rebellion.
Tarkin consitantly bragged to Ackbar what the Empire could do, all the while Ackbar was learning Imperial Stratigies, tactics, and even had on some occasions to read classified information.
best of luck
edit: my guess Ackbar was enslaved before the bombardment of Mon Cal cities. And might have been one of the passive resistors that caught the eye of a certain Moff. It makes sense that Grahm Muff Tarkin coudl have had some authority of the Mon Cal system
[This message has been edited by K_Kinnison (edited May 11, 2001).]