It shall be unlawful for any person to import, in violation of any regulation adopted pursuant to section
971d
(c) or (d) of this title, from any country, any fish in any form of those species subject to regulation pursuant to a recommendation of the Commission, or any fish in any form not under regulation but under investigation by the Commission, during the period such fish have been denied entry in accordance with the provisions of section
971d
(c) or (d) of this title. In the case of any fish as described in this subsection offered for entry in the United States, the Secretary shall require proof satisfactory to him that such fish is not ineligible for such entry under the terms of section
971d
(c) or (d) of this title.