SlackBuildsOrg/system/fish

fish (Friendly Interactive SHell) is a user friendly command line shell
for UNIX-like operating systems.

This SlackBuild automatically adds fish to /etc/shells.

To use fish as your login shell, run this command:

$ chsh -s /usr/bin/fish

To remove fish from the /etc/shells, in case of fish removal, please run:

$ su -c "sed -ri '\|^/usr/bin/fish$|d' /etc/shells"

This package will potentially conflict with the /usr/games/fish binary
from the y/bsdgames package.  In a stock installation with default PATH
ordering, /usr/bin should be checked before /usr/games, so it shouldn't
be an issue, but we thought it was worth noting just in case.