You are the fifth

A man saw a fisherman standing in a lake with a mirror. "Excuse me," he said, " but could you tell me what you're doing?"
"I'm fishing."
"With a mirror?" the first man asked.
"Sure--it's a new invention. I'm going to make a fortune."
"Could you tell me how it works?"
"Okay, but it'll cost you a hundred dollars."
The first man was so curious that he handed the fisherman the money.
"Now, show me how it works," he said.
"Well," the fisherman began, "you aim the mirror into the water, and when a fish goes by, you startle  him the rays of light reflected from the mirror. The fish gets confused and then you grab him."
The first fellow was shocked.
"You can't mean to tell  me that's how you fish. It's ridiculous! How many have you caught?"
"You're the fifth today!" replied the fisherman.