When fish are placed outside the pool tube, they end up inside the pool.
This seemed fixed at first, but the problem repeats itself after validating the mission.
To reproduce, go to the open space reached by the small cave.
Inside place a shark and validate the mission.
Upon validating the mission the shark will be inside the pool.
Edit: Noticed it also occurs without validating.
Selecting fauna goes well, upon changing the type of fish the fish will not show at the fish box.
If someone is able to reproduce this, please do so.