(1) Immediately after the establishment of the retirement system, the actuary shall recommend to the board of trustees, and the board shall adopt, mortality and service tables for use in all calculations in connection with the retirement system.
(2) At least once in each six-year period, the actuary shall make an actuarial investigation into the mortality, service, and compensation experience of the members and beneficiaries of the retirement system, and taking into account the results of such investigation, the board of trustees shall adopt for the retirement system such mortality, service, and other tables as are deemed necessary. The board of trustees shall begin using the tables on July 1 of the year following the action of the board of trustees.