What is the name of lower swimming organ on a fish?

The lower swimming organ on a fish is called the anal fin.

It's located on the underside of the fish, near the tail. While not as crucial for propulsion as the tail fin, the anal fin helps with:

* Stabilization: Keeping the fish upright and balanced

* Maneuvering: Assisting in turning and stopping

* Braking: Slowing down the fish

Some fish have additional fins, but the anal fin is always present.