While Mohamed El-Erian, heir apparent to Pimco co-founder Bill Gross, did not give a reason for his recent departure, the shakeup provides insightful glimpses into the industry for mutual fund and ETF managers.

El-Erian's departure, after all, comes as customers withdrew $40.4 billion of money from Pimco's flagship Total Return Fund last year, a record amount for the $2 trillion manager, according to Morningstar. Pimco's open-end mutual fund lineup suffered more than $30 billion in net outflows last year, according to Morningstar, which compares with $62.7 billion worth of net inflows in 2012. Pimco's taxable bond funds, representing the largest share of the firm's mutual fund business, suffered net outflows of more than $44 billion last year. The fixed-income funds had $55.4 billion in net inflows in 2012.

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