Brine shrimp are small shrimp that live in salt water. Brine shrimp are Artemia, a genus of aquatic crustacea which has changed little (externally) since the Triassic period. They can often be found in saltwater ponds and marshes, and cannot live very long in fresh water. "Artemia" avoid most types of predators, such as fish, because they live in waters of very high salinity: (25 parts per thousand). The optimum for "Artemia" is 100 to 150 parts per thousand. The shrimp grow to be about one centimeter long. Females tend to be larger than males.