It shall be unlawful for any person, firm, corporation or association to sell or offer for sale, to take from any reef or have in his possession or to buy or offer to buy any oysters whose length is less than three inches, taking into consideration the five percent allowance as provided for by law, except when the legal size of oysters is reduced by a regulation duly promulgated by the Commissioner of Conservation and Natural Resources as otherwise provided for under this title; provided, that nothing in this section shall be construed so as to apply the provisions hereof to the taking of oysters from private reefs by the owners or lessees of such private reefs.