NEW YORK--(BUSINESS WIRE)--Smaller investment-grade corporate bond issues, under $500 million, trade materially less frequently than larger issue bonds among a sample study of the underlying holdings of five major U.S. corporate bond ETFs, says Fitch Ratings. Low trade frequency has the potential to become a more significant issue under market stress, which Fitch believes is a growing risk as bond inventories are reduced and possible interest rate hikes lie ahead. While measuring bonds' attribu