Which Aesop's Fable Is About "Grasping At A Shadow But Losing The Substance"�?

A dog stole a bone from the butcher and trotted homewards with it. As he was passing the stream, he caught sight of his reflection in the water. There he saw what looked like a bigger dog, holding a bigger bone than his own. He immediately dropped his bone and jumped into the water to fight the "other dog." He got soaking wet, couldn't catch his opponent – who seemed to disappear as soon as he jumped in – and finally crawled out, exhausted and bewildered. At this point he noticed that his own bone had also gone, since it had been swept away in the current.
This fable is about the importance of holding on to the real things we have and not being carried away by illusions. In another version of this fable, the dog tries to catch the reflection of the moon in the water, believing it to be a big ball.