you can throw some clay into a hole to fill it back.
To catch fish, just use a fishing rod when facing a river or lake, it might take some tries depending on the spot. That system will be fleshed out in the future with bait and hints for fishing spots.
The hole fill doesn't work on water though, so if I dig a water trench too large or oddly shaped, I end up being limited in my building or sometimes trapping myself lol
