Fish inherits from `template_gaia_fish.xml`, not from `template_unit_fauna.xml`, therefore their current file names (`fauna_fish*`) are incorrect. This patch moves them into a subfolder of their own (`gaia/fish/`), because although only three types of fish exist right now, it's not inconceivable many more will be added in the future.
Cf. `gaia/ruins/` and `gaia/treasure/`, which contain files that inherit from `template_gaia_ruins.xml` and `template_gaia_treasure.xml`, respectively.
Apply the patch, then run the following command to adjust all map files:
```
find binaries/data/mods/public/maps/ \( -name '*.js' -o -name '*.json' -o -name '*.xml' \) -print0 | xargs -0 sed -i \
-e 's,gaia/fauna_fish_tuna,gaia/fish/tuna,g' \
-e 's,gaia/fauna_fish_tilapia,gaia/fish/tilapia,g' \
-e 's,gaia/fauna_fish,gaia/fish/generic,g'
```
See also D2254.