I don't use fish for shell scripting, but I'm enjoying it as my primary environment after making these adjustments..

Status codes and argument lists:

    $status  # replaces $?
    $argv    # replaces $@

Aliases are just functions (configure your startup in ~/.config/fish/config.fish):

    # alias ls="ls -lrth"
    function lr; ls -lrth $argv; end

For-loops are familiar:

    # for n in one two three; do echo $n; done
    for n in one two three; echo $n; end

The lack of '!$' confounded my hard-wired fingers until I settled on Alt-u to avoid up-arrows (see /usr/share/fish/functions/fish_default_key_bindings.fish):

    bind \eu history-token-search-backward  # replaces !$
    bind \ei history-token-search-forward   # bonus fun

The remaining price for fish's pseudo-telepathic assistance is the occasional frustration with applications that rely on the value of a user's default shell (/etc/passwd).

Your script should have "#!/bin/bash" at the top, which tells the shell what interpreter you want it ran with. So, yes?