Abstract The pet trade is a significant source of introductions of non-indigenous aquatic species, such as crayfish. To test whether legislation that regulates the ownership of ornamental animals for aquariums had the desired effect of reducing the availability of those pets, classified advertising websites were monitored for sales of crayfish in jurisdictions with and without legislation regulating the ownership of crayfish. Advertisements from Canadian provinces with legislation against owning crayfish were compared to provinces without such legislation. The population adjusted number of advertisements for crayfish, and number of distinct sellers of crayfish, was significantly lower in one of two provinces that prohibited crayfish compared to provinces that permitted crayfish. This mixed outcome suggests that legislation alone does not consistently reduce online trade in crayfish.