Ray,
Id you are referring to the Japanse sunken Gardens next to Brackenridge Park, I remember hearing that the landscaper of Japanese decent had koi in those gardens prior to WW II...but it has been 20 years and I may have that wrong. I remember taking the sky ride in Brackenridge Park and seeing the huge koi below in those gardens.....of course "huge" is relative but they sure seemed large back then (86 - 87 ish).
I'll see what I can dig up on that. Cheryl may know more as well since she grew up there..
Steve