This is the easiest way to get small fish in Subnautica for food or water.
Create a gravity trap
First, you need a special trap. To create it you need:
These resources can be found near the Grassy Plateau on the way to Aurora. A scanner is required to scan fragments.
Fishing
After that, head to a safe sandbank and find an area with a lot of fish, then discard the trap. However, you can throw it anywhere - it's your choice.
