No officer shall be allowed any emoluments or compensation, aside from his salary as fixed by this Charter, or by ordinance, and all fees received by him in connection with his official duties shall be paid by him into the city treasury. Provided, that any rewards received by any member of the police or other departments, for the apprehension or conviction of persons charged with crime, may be retained, except as to any part of such reward as may be provided by ordinance to accrue to the benefit of, and be paid into, the pension fund or funds.