In the last trading session, U.S. stocks were slightly subdued. Among the top ETFs, investors saw SPY shedding about 0.13%, DIA losing about 0.3% and QQQ move lower by 0.05% on the day.Two more specialized ETFs are also worth watching as both saw trading volume that was far outside of normal. In fact, both these funds experienced volume levels that were more than double their average for the most of the last trading session. This could make these ETFs ones to watch out for in the days ahead to see if this trend of extra-interest continues.VDE: Volume 3.27 times averageThis energy ETF was under the microscope yesterday as about 1.59 million shares changed hands. This compares to the average trading volume of around 485,580 shares and came as VDE lost about 1% in the session. Oil prices are on track for the first yearly decline in three years thanks to the ongoing concerns of a supply glut. The fund has lost about 16.7% in the past one month.VIG: Volume 3.09 times averageThis U.S. equities ETF, consisting of stocks of companies that have a record of increasing dividends over time, was in the spotlight yesterday as 4.49 million shares moved hands compared with an average of roughly 1.52 million shares a day. The fund lost about 0.05% in the last trading session and has been down about 10.7% in the past one month.Want key ETF info delivered straight to your inbox?Zacks’ free Fund Newsletter will brief you on top news and analysis, as well as top-performing ETFs, each week. Get it free > Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report SPDR-DJ IND AVG (DIA): ETF Research Reports VIPERS-ENERGY (VDE): ETF Research Reports VANGD-DIV APPRC (VIG): ETF Research Reports SPDR-SP 500 TR (SPY): ETF Research Reports NASDAQ-100 SHRS (QQQ): ETF Research Reports To read this article on Zacks.com click here. Zacks Investment Research Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report