An exchange traded fund indexed to U.S. corporate high-yield bonds saw trading volume surge Thursday but the spike likely reflected a large trade that was made the previous day, according to an analyst who tracks ETF trading and liquidity.

More than 22 million shares of SPDR Barclays Capital High Yield Bond ETF (NYSEArca: JNK) had traded hands in afternoon dealings Thursday. Over the past three months, JNK has averaged daily volume of about 4.8 million shares, so trading in the ETF was more than 400% of the usual pace. [ETFs Bring Liquidity to High-Yield Bonds]

Paul Weisbruch, head of ETF/options sales and trading at Street One Financial, said a trade of over 19 million shares hit the tape in Thursday’s premarket before the opening bell.

“That is a reflection that the trade itself likely was consummated yesterday,” Weisbruch said.

It appears a customer sold out of large position in JNK on Wednesday but the trade was reported to the marketplace today, he added.

The JNK trade happened at $39.41 a share, Weisbruch said, while the ETF traded in a range between $39.42 and $39.65 a share in Thursday’s regular session.

A spokeswoman for State Street Global Advisors, which manages JNK, didn’t immediately return a request for comment on Thursday’s volume spike.