There are approximately 830 exchange-traded funds listed in the U.S., as of mid-September, and with the completion of the acquisition of the American Stock Exchange by the New York Stock Exchange, 680 of those ETFs now trade on the New York exchange's electronic platform, NYSE Arca. The deal was completed yesterday.

NYSE Arca already had close to $317.5 billion in ETF and exchange-traded note assets under management. Even before the acquisition, that $317.5 billion in ETF assets made it the leader among all exchanges in the hotly contested battle for ETF market share.

Now with the addition of the Amex's 416 ETF and 13 ETN listings being made official, the combined ETF listings business at NYSE Arca will grow to more than 680 ETFs and 90 ETNs, according to exchange data. This does not include NYSE's 344 ETF listings in European markets.

It is not hard to understand why exchanges are battling intensely for control of ETF listing and trading. As of the end of August, ETF trading had grown to represent more than 31% of all U.S. equities trading (see related story).

What's more, ETFs reached above the 40% threshold of U.S. equities trading during the particularly rocky market ride of the week beginning Sept. 15. These days it is also common to see some of the most well-known and heavily traded ETFs, such as SPDRs (AMEX: SPY) and PowerShares QQQ (Nasdaq: QQQQ), among the most actively traded equities on any given day in the market.

Big changes are still ahead in regards to the acquisition of Amex. In December, the Amex equities trading platform will piggyback off NYSE Euronext technology, and its existing systems will be scrapped. NYSE Euronext also plans to relocate the Amex options trading floor operations to the NYSE options trading floor during Q1 2009, as well as transition the electronic options trading to NYSE Euronext technology.