The unarmored three-spined stickleback (Gasterosteus aculeatus williamsoni) is a fish that is found only in North America; its recognised range is southern California, though there are isolated reports of it occurring in British Columbia and Mexico; These subspecies actually represent three examples from the enormous range of morphological variation present within three-spined sticklebacks. These fall into two rough categories, the andromous and the freshwater forms.