Use fish shell

modules/nixos/default.nix

@@ -1,6 +1,5 @@
-# Add your reusable NixOS modules to this directory, on their own file (https://nixos.wiki/wiki/Module).
-# These should be stuff you would like to share with others, not your personal configurations.
 {
-  # List your module files here
-  # my-module = import ./my-module.nix;
+  imports = [
+    ./fish.nix
+  ];
 }

modules/nixos/fish.nix

@@ -0,0 +1,4 @@
+{ pkgs, ... }: {
+  programs.fish.enable = true;
+  users.defaultUserShell = pkgs.fish;
+}