In the last trading session, U.S. stocks ended on a weaker note on renewed global growth worries. Among the top ETFs, investors saw SPY go down 0.95%, DIA lose 0.65% and QQQ shed 1.13% on the day.

Two more specialized ETFs are worth noting 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 recent trading session. This could make these ETFs the ones to watch out for in the days ahead to see if this trend of extra-interest continues:

(UBT Quick QuoteUBT - Free Report) : Volume 5.89 times average

This leveraged long-term government bond ETF was in focus on Friday as almost 98,000 shares moved hands. This compares to an average trading day of 17,000 shares. UBT gained about 1.6% in the session.

The movement can largely be attributed to a fall in long-term treasury yields. Funds with leveraged factor tacked on them provide outsized returns in a very short period of time. UBT was up over 5.6% in the past one-month period.

(FKU Quick QuoteFKU - Free Report) : Volume 3.36 times average

This U.K. ETF was under the microscope on Friday as nearly 68,000 shares moved hands. This compares to an average trading volume of 20,000 shares and came as FKU lost 4% in the session.

The big move can largely be blamed on a potential Brexit weighing on stocks with June 23 drawing closer when Britain will vote on whether the U.K. should remain a member of the EU. This can have a big impact on the U.K. stocks like the ones we find in this ETF portfolio. In the last one-month period, FKU was down about 0.6%. The fund currently has a Zacks ETF Rank #3 (Hold).

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