need to get fish frozen for a long time under -20C

Official document:

https://www.health.state.mn.us/communities/environment/food/docs/fs/fishrawfs.pdf

Exemptions: Some fish species or products do not have specific parasite hazards and are exempt from aquaculture or freezing requirements. These include:  Tuna of the species Thunnus alalunga, T. albacares, T. atlanticus, T. maccoyii, T. obesus, or T. thynnus. Common names of these fish include: Yellowfin, Bigeye, and Northern and Southern Bluefin; Fish eggs which have been removed from the skein and rinsed; Molluscan shellfish and shucked scallops