The U.S. junk-bond rout deepened Monday, with the bonds of dozens of low-rated companies falling anew and the shares of some large fund-management firms tumbling as well. The declines reflected gathering concerns about risky companies’ access to financing, traders’ capacity to sell bonds without causing prices to fall, and ripple effects from the closure of a junk-bond mutual fund. Together, the concerns are feeding investor fears that the U.S. mutual-fund industry could face outflows that will test funds’ capacity to meet investor redemption requests. The iShares iBoxx $ High Yield Corporate Bond exchange-traded fund, the largest junk-bond ETF by assets, was down about 1.5% Monday, after shedding 2% on Friday in its worst plunge since 2011, to trade at $78.34 a share. The fund’s operator, BlackRock Inc., BLK -0.99 % said it held conference calls Monday after receiving questions from investors about liquidity and the health of the high-yield […]