Any fiduciary who conducts or is liquidating the business or is selling the assets of any company included in § 12-249, § 12-256 or § 12-264 shall be subject to the filing of returns in accord with, and to the payment of taxes imposed by, this chapter in the same manner and to the same extent as if the business were being conducted or liquidated or assets sold by agents or officers of such company. The return of a fiduciary who has been appointed during a taxable period under said sections, or following such period but on or before the last day upon which a return may be filed for such period without penalty, shall include complete information with respect to that part of such period during which the company conducted the business as well as that part of such period in which the fiduciary himself was acting and taxes shall be paid by the fiduciary for both parts of such period.