For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:eroca/openSUSE_Tumbleweed/home:eroca.repo
zypper refresh
zypper install fish
For 16.0 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:eroca/16.0/home:eroca.repo
zypper refresh
zypper install fish
For 15.7 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:eroca/15.7/home:eroca.repo
zypper refresh
zypper install fish