Found this;
WAC 232-12-027
(9) A game farm license is not required for captive-bred mink, Mustela vison, and captive-bred silver fox, Vulpes fulva, lawfully acquired from a licensed breeder or fur farm and held for fur farming purposes.
16.72.010
Definitions.
As used in this chapter:
"Director" means director of agriculture.
"Department" means department of agriculture.
"Person" includes any individual, firm corporation, trust, association, copartnership, society, or other organization of individuals and any other business unit, device or arrangement.
"Fur farming" means breeding, raising and rearing of mink, marten, fox and chinchilla in captivity or enclosures.
[1955 c 321 § 2.]
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16.72.020
Quarantine controls.
Fur farming shall be deemed an agricultural pursuit and the director is hereby authorized to exercise quarantine controls over such farms in accordance with the provisions of this title. Facilities available to the department may be used by the director in carrying out the provisions of this chapter.
[1955 c 321 § 3.]
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16.72.030
Fox, mink, marten declared personalty.
All fox, mink and marten that have been lawfully imported or acquired, or bred or reared in captivity or enclosures, are declared to be personal property. Any person hereafter acquiring any such fur bearing animals in the wild state, shall within ten days furnish satisfactory proof to the director that such animals were lawfully obtained. Such wild animals shall not become personal property under the provisions of this section until such proof is furnished.
[1955 c 321 § 4.]
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16.72.040
Branding — Recording.
The owners of any fox, mink, or marten may mark them by branding with tattoo or other marks for the purpose of identification, but no person shall be entitled to ownership in or rights under any particular branding marks unless and until the branding marks are recorded with the department in the same manner and with like effect as brands of other animals are recorded as provided in *chapter 16.56 RCW.
Doesn't appear to me you need a license anymore then any other livestock.
