April 24 (Reuters) - Short interest on the Nasdaq rose

0.5% in mid-April, the exchange said on Friday.

As of April 15, short interest rose to 20,498,266,178

shares, compared with 20,395,670,061 shares as of March 31.

Investors who sell securities "short" borrow shares and then

sell them, expecting the stock to fall so they can buy the

shares back at the lower price, return them to the lender and

pocket the difference.

Shorting can also be part of a hedging strategy.