Investment management firm Rathbone Brothers saw funds under management (FUM) climb 7.3% in the first quarter of 2010 to £14.05bn.Acquired inflows on the Investment Management side totalled £241m in the first quarter while net organic growth was £96m, Inflows plus net organic growth represents a net annual growth rate of 11%, compared to a growth rate of 8.1% in 2009. Net organic growth on its own ran at an annualised rate of 3.2% in the first quarter, versus a growth rate of 5.8% in 2009.Net operating income in Rathbone Investment Management was £29m, up from £27.3m in the first quarter of 2009, with commissions running high ahead of the end of the tax year; commissions have since returned to more normal levels.On the Unit Trust Management side FUM rose to £942m at the end of March from £935m at the end of 2009, despite net redemptions of £42m.Net operating income in Rathbone Unit Trust Management rose 5.6% to £1.9m in the first quarter from £1.8m a year earlier.