これをする。
which fish chsh -s /usr/local/bin/fish
エラー
chsh: /usr/local/bin/fish: non-standard shell
が出た場合
sudo vi /etc/shells
して、
# List of acceptable shells for chpass(1). # Ftpd will not allow users to connect who are not using # one of these shells. /bin/bash /bin/csh /bin/ksh /bin/sh /bin/tcsh /bin/zsh /usr/local/bin/fish # <-これを追加