This occurs because, out of the box, the Rubies installed through RVM aren't added to your path. When you run any RVM command, it adds the paths relative to the ruby version you're using to $PATH. RVM seems to take care of bash and zsh but doesn't have built-in support for correcting the paths for your dot files.
Here's an example of my path before an RVM command:
/Users/grant/pear/bin /usr/local/sbin/ /Users/grant/.rvm/bin /usr/local/bin /usr/bin /bin /usr/sbin /sbin /usr/local/git/bin /usr/local/go/bin
Here's an example of my path after running 'rvm':
/Users/grant/.rvm/gems/ruby-2.2.0/bin /Users/grant/.rvm/gems/ruby-2.2.0@global/bin /Users/grant/.rvm/rubies/ruby-2.2.0/bin /Users/grant/pear/bin /usr/local/sbin/ /Users/grant/.rvm/bin /usr/local/bin /usr/bin /bin /usr/sbin /sbin /usr/local/git/bin /usr/local/go/bin
The bottom line is that you'll want to add the .rvm files to your path depending on the version you default to. This post helped me figure out how to do that. You can append the paths that RVM adds to your fish profile with:
set -g -x PATH $PATH <paths_to_add>
Example from above:
set -g -x PATH $PATH /Users/grant/.rvm/gems/ruby-2.2.0/bin /Users/grant/.rvm/gems/ruby-2.2.0@global/bin /Users/grant/.rvm/rubies/ruby-2.2.0/bin
To have this run every time you load fish, add the above command to ~/.config/fish/config.fish. Alternatively, you can add the rvm command to your fish config and have it load it for you.
Hope this helps!
-Grant