The species profile is incorrect on this site ....that is one of the issues the new owner is going to be working on (hopefully) the rainbow shark may only get to around 6" but it requires a much bigger tank:
http://www.fishlore.com/profiles_rainbow_shark.htm
http://www.peteducation.com/article.cfm?cls=16&cat=1953&articleid=2602
http://www.petresources.net/fish/cyprinid/epa_fre.html
you are doing the right thing by coming here for advice..there are many knowledgable people here who will help you, but along with advice given look up a few you are interested in and see wht you can find out.
Good luck with your choices.
http://www.fishlore.com/profiles_rainbow_shark.htm
http://www.peteducation.com/article.cfm?cls=16&cat=1953&articleid=2602
http://www.petresources.net/fish/cyprinid/epa_fre.html
you are doing the right thing by coming here for advice..there are many knowledgable people here who will help you, but along with advice given look up a few you are interested in and see wht you can find out.
Good luck with your choices.