Cannot access last element of a list of GameObjects

As the title describes, I'm having trouble accessing the last element of a list.

I have a list here of gameobjects:

     List<GameObject> asteroidPrefabs = new List<GameObject>();

And an array of the objects which is assigned from the unity editor, say we have 8 of them:

     public GameObject[] asteroids;

And then I initialize the objects and add them to my asteroidPrefabs list:

         for (int i = 0; i < asteroids.Length - 1; i++)
         {
             asteroidPrefabs.Add(asteroids[i]);
         }

I initiate them in this function:

     public void InstantiateAsteroid(Vector2 position, Quaternion rotation)
     {
         prefabIndex = Random.Range(0, asteroids.Length - 1);
         Instantiate(asteroidPrefabs[prefabIndex], position, rotation);
     }

Here's the problem: When the randomizer picks the last element, which is 7 (because I have 8 objects assigned to the list).

It outputs this error:

 ArgumentOutOfRangeException: Argument is out of range.
 Parameter name: index

So I cannot spawn my game object of the last element. Is there a way to fix this?