Fidelity has lost the second fund manager of its flagship Fidelity American fund in 10 months, following Fergus Shiel's resignation.

It is the third time in a year that Fidelity has found itself in need of someone to manage one of its most important funds. Shiel took over management of the US equity fund last June following the departure of John Muresianu to set up a hedge fund. His place will now be taken by Jason Weiner, who is part of Fidelity's Boston-based US equity team and manages other funds for the group.