1. Start your own mod. You've probably done that already.
2. Copy the goldfishgenerator.ob2 from the main mod into your own mod, into the same subdirectory.
3. Open the file using the import button.
That should do it! If you're for some reason unable to even export an object (your exported object never shows up in the import screen), then it might be possible that the mod directory is copy protected, or that it doesn't even exist.