This is a show created to promote a gacha game that ended service just half a year after the show aired. In the future, fish have disappeared from the Earth's oceans. In response to this, the government takes the only rational course of action: create oceans in space to be fished from. You might be thinking, "Surely if we have the technology to create oceans in space that house fish, it would be much easier to just repopulate the Earth's oceans, or at least create fisheries on Earth right?". Or you might also be thinking, "The amount of money it would take to create these space seas, and launchrockets into space every time you want to fish from them, the entire thing would be so cost prohibitive nobody would be able to afford to buy fish in the first place, right?".

Unfortunately, I don't have any good answers for you, and neither does the anime.

However, the main character is extremely cute, and I love her voice. The show is pretty funny too, often unintentionally.
If you want to watch a funny show with cute girls voiced by amateurs, then turn your brain off, and give this show a watch.