The bonds of each issue shall be dated.  They shall bear interest at not more than six per cent per year, payable annually.  They shall mature at a time determined by the governing authority of the parish, but not more than forty years after date of issuance.  They may be made redeemable before maturity, at the option of the parish, at a price and under terms and conditions fixed by the governing authority thereof prior to the issuance of the bonds.