Just over a centimeter in size, the adult brine shrimp Artemia is an extremely wellknown animal because of its importance as a food source for fish and crustaceans raised in home aquariums, aquaculture systems, and in laboratories. One can buy brine shrimp at practically any pet display. It looks like a powdery brown substance but in reality the substance is thousands of cysts—eggs surrounded by protective cases. When added to water, these cysts will hatch into shrimp nauplii within a few hours.
Although the cysts are very small (about 200 micrometers in diameter; 50 could fit on the head of a pin) at times they become so numerous that they form large red-brown streaks on the surface of the lake. Under optimum conditions of food supply and lack of stress from increasing salinity or decreasing dissolved oxygen, fertilized female shrimp may produce eggs that hatch soon after emerging from the ovisac to produce nauplius larvae, which is known as ovoviparous reproduction. If conditions are perfect, the female can live as long as 3 months and produce as many as 300 live nauplii or cysts every 4 days. However, the cold spring-time temperatures and variable food supply in Great Salt Lake usually limit the population to two or three generations per year.
Under magnification, the elongated shape and eleven pairs of limbs give this organism a shrimplike shape, but Artemia actually falls into an order of primitive crustaceans. Various pigments from the phytoplankton that the shrimp eats give hues of blue, green, and red to the otherwise transparent body.
Because brine shrimp are so desirable as a food source they are found naturally in only about 250 locations around the world, in water bodies so salty that predators and competitors for the same food cannot survive. The only companion life to the brine shrimp in these ponds are a few species of bacteria and algae, which provide forage for the shrimp.
In the United States, in areas such as the Great Salt Lake, the brine shrimp's yearlong life cycle usually begins in early spring. After hatching, the larvae will go through 15 molts before it reaches the adult form. These begin to die by October and most will be gone by December. In the period from May to December females will give birth to either live nauplii or, if conditions are wrong for larvae survival, they will lay a number of cysts. These will be dispersed by winds and waves. Often the cysts drift to shore, where they remain until spring rainfalls wash them back into the water. These will later hatch when water, temperature, salinity, oxygen, and other seasonal conditions are right.
It is this ability of the brine shrimp cysts to remain dormant for long periods of time and then be easily hatched that has made them an easy live food for the use of tropical fish hobbyists and aquaculturist as well as a valuable organism for research. These cysts can withstand wide fluctuations in temperature due to their ability to lose, and regain, practically all of their intracellular water. For at least a century the brine shrimp, because of its characteristics and its short life span, has been useful to a variety of researchers in genetics, histology, toxicology, radio biology, biochemistry, molecular biology, and ecology. Because the cysts are also very small and require no food, they were chosen as test organisms for the early space experiments. Cysts housed both within and outside the U.S. Apollo and the U.S.S.R. Cosmos spacecraft helped scientists determine the effects of ultraviolet radiation on living cells.
Despite the fact that brine shrimp have been studied ever since 1755, when they were first observed in the salt ponds of Lymington, England, there were major gaps in knowledge about the organism, particularly its nutritional value, up to the late 1970s. Brine shrimp have been found to be a critical food for certain fish at early stages to insure good survival and increased growth. An international group of scientists from Rhode Island, Wales, Spain, and Belgium investigated many of the still unanswered questions about the differences among brine shrimp strains and found that geographical location and water quality are important factors in determining the organism's composition of fatty acids, proteins, pesticide concentrations, and other substances. If anyone is having trouble with a brine shrimp strain and suspects that it is the cause of problems in survivability and growth of fish, a standard stock is available from the Artemia Reference Center in Ghent, Belgium, which has been determined to be free of pesticides and to maintain good growth and survival in organisms to which it is fed.