Vanguard's first four fixed-income exchange-traded funds began trading on the American Stock Exchange Tuesday. The Total Bond Market ETF ( BND), Short-Term Bond ETF ( BSV), Intermediate-Term Bond ETF ( BIV) and Long-Term Bond ETF ( BLV) are structured as a separate share classes of established, broadly diversified bond index funds. All four of the bond ETFs carry expense ratios of 0.11%. Vanguard is the nation's second-largest mutual fund manager but is a relatively small player in the ETF industry, with approximately $23 billion in domestic and international stock ETFs. The company had filed plans for the ETFs with the Securities and Exchange Commission in January.