Investment of the fund is under the supervision of the state investment board in accordance with chapter 21-10. The moneys must be placed for investment only with a firm or firms whose endeavor is money management, and only after a trust agreement or contract has been executed. Investment costs may be paid directly from the fund, and are hereby appropriated for that purpose, in accordance with section 21-10-06.2. All interest and earnings on funds administered by the board must be credited to the fund.