Assets in U.S. listed Exchange-Traded Funds (ETF) and Exchange-Traded Notes (ETN) rose about 31 percent in March, according to the latest data from National Stock Exchange.

Assets in U.S. listed ETFs and ETNs totaled about $1.08 trillion at March 2011 month-end, up 31 percent over March 2010 month-end when assets totaled almost $820 billion.

ETF/ETN net cash inflows for the month of March totaled approximately $11.2 billion.

Meanwhile, ETF/ETN notional trading volume during March 2011 totaled almost $1.8 trillion, representing almost 31 percent of all U.S. equity trading volume.

At the end of March 2011, the number of listed products totaled 1,173 compared to 971 listed products at the same time last year.

An ETF is an investment fund traded on stock exchanges, much like stocks, whereas an ETN is a senior, unsecured, unsubordinated debt security issued by an underwriting bank.