Koi is a good idea but not very realistic to put in a tank...
they r often rather big compare to other freshwater fishes....
they usually keep in ponds more then tanks....
may be baby-koi is a nce idea?
James C Chen
Principal Engineer as SDET, Connected Services
HTC Corporation
88 Section 3. Zhongxing Road
Xindian District, New Taipei City 231, Taiwan
www.htc.com