Bill Gross
Bill Gross has quit Pimco, the world's largest bond fund, which he co-founded. Reuters

Janus Capital Management shares have rocketed 40% in the US pre-market open after the co-founder of the world's largest bond fund, Bill Gross, announced that he is leaving Pimco to join the smaller asset management group.

The jump in the stock price to around $14.40 means Gross' news has added $750m (£461m, €590m) onto Janus' market capitalisation.

But the news that Gross is leaving Pimco also impacted other stocks.

His former Pimco protégée Mohamed El-Erian quit the firm in early 2014, after a high profile fallout with his boss, and joined Allianz. However the Allianz stock is down by 6.7% and has wiped around $3.77bn on market cap over the news.

Pimco is reportedly under investigation by the US Securities and Exchange Commission (SEC) over whether investors were given inaccurate information about the performance of its flagship fund.

Gross has been questioned by investigators over his management of a multi-billion exchange-traded fund. Pimco said it was working with the SEC and did not think its pricing had been inappropriate.

"Bill Gross has an exemplary track record with decades of success and he will offer an exceptional approach to navigating today's increasingly risky markets with a focus on macro, unconstrained strategies," said Richard M. Weil, chief executive of Janus Capital Group.

"His involvement provides Janus a unique opportunity to offer strategies and products that are highly complementary to those already managed by our credit-based fixed income team

"With Bill leading our global macro efforts and Gibson our credit-based fixed income team, I am confident Janus will be able to meet the needs of virtually any client."