Allows you to put fish in water and breed them. Revolutionary technology.
In your image, I see an inserter near the water, leading to the machine, however in game this doesn't appear to do anything. Is this meant to catch the fish?
It's a secret/easter-egg homage to davemcw (https://forums.factorio.com/memberlist.php?mode=viewprofile&u=1868) who wrote the blueprint-string mod (https://mods.factorio.com/mods/DaveMcW) and has done lots of other good things for factorio.
He uses an inserter in this fashion on his forum avatar.
Great job spotting it :-)
And you are correct, it does not work.
