What is a Yellow fish with black tail spot large stomach and 1 inch length He looks like some kind of molly?

Based on your description, it's difficult to pinpoint the exact species of fish. However, here are some possibilities that match your description, keeping in mind that visual identification without a picture is challenging:

* Yellow Molly (Poecilia sphenops): They come in various colors and patterns, including yellow with a black tail spot. They are known for their large, rounded bellies and can grow to around 2 inches.

* Sailfin Molly (Poecilia latipinna): These are similar to Yellow Mollies, but with a more prominent dorsal fin. They also can be yellow with a black tail spot.

* Black Skirt Tetra (Gymnocorymbus ternetzi): Though generally black, they have a distinctive "skirt" of fins that can appear yellow in some varieties. They can also have a black tail spot and grow to about 2.5 inches.

To narrow it down further, consider these questions:

* Where did you find this fish? Knowing its origin (aquarium, pond, wild) can help.

* Does the fish have any other distinct markings? (Stripes, spots, etc.)

* What shape are the fins? (Long, pointed, rounded)

* How does it behave? (Active, shy, peaceful)

A picture of the fish would be most helpful in identifying it accurately.