The world's largest mutual fund company has agreed to voluntarily pay a $42m (€31.8m) penalty to investors for accepting gifts from investment banks, but regulators are keeping the investigation open.

Fidelity Investments said on its website today that it would pay the penalty after an 18-month-long investigation by John Martin, a former judge. Martin found that some employees on the firm's equity trading desk had accepted gifts from Jefferies' salespeople in violation of the company's policies. The employees that accepted the gifts left the company or moved into other departments, Fidelity said.