It doesn't work out of the box because some files are installed in wrong locations. I had to cp /usr/share/services/fish.protocol usr/kde/3/share/services/ and cp /usr/lib/kde3/kio_fish.* /usr/kde/3/lib/kde3/ to make it work. Edi.
The kde-env ebuild adds /usr to KDEDIRS, enabling kde apps to work when installed in /usr. Please move kio_fish back to /usr, check that kde-base/kde-env-3-r1 is installed, and to make sure its changes take effect, run env-update (just in case) and restart kde. If it still doesn't work, tell me.
had the same problem. resolved it by copying /usr/share/services/fish.protcol to /usr/kde/3/share/services nothing else was required...
So services/ isn't scanned for all KDEDIRS values? hm... I rather think it is in latest cvs.. I'll have to look into it.
kio_fish is part of kde 3.1, to be released in a few days. So since I cannot reproduce this problem, and you have a local fix easily available, I'm not interested in fixing it.