The three-spined stickleback, is a fish native to most inland coastal waters north of 30°N. Most populations are anadromous (they live in seawater but breed in freshwater or brackish water) and very tolerant of changes in salinity, a subject of interest to physiologists. For this reason, three-spined stickleback are easy to find in nature and easy to keep in aquaria.
Fun Fact They are capable of perceiving ultraviolet wavelengths of light invisible to the human eye and use such wavelengths in their normal habits.