"This news has likely led to the significant selling off of asset manager stocks today with many of the stocks we track down (3 percent to 5 percent) versus flat for the S&P 500 index," Wells Fargo analyst Christopher Harris said in a research note.

"We wouldn't think the Fidelity funds in and of themselves would lead to much change with respect to asset flows, but investors are likely concerned about the follow-on effects," Harris said. "For instance, do other passive index providers lower their fees in response?"

Publicly-traded asset managers whose shares declined on Wednesday include BlackRock down 4 percent at midday, Legg Mason Inc down 5 percent, and T. Rowe Price Group down 3 percent.

Boston-based Fidelity said the Zero Total Market Index Fund and the Zero International Index Fund will be available to investors on Friday.

"Investors will pay a 0.00 percent fee, regardless of how much they invest in either fund, while gaining exposure to nearly the entire global stock market," Fidelity said.