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Perhaps no other aquatic species contributes to oceanic ecology like the Brine Shrimp. Brine shrimp is a form of zooplankton. It is versatile in its physical and chemical characteristics. Its hardiness and survivability make it very special for preservation. It is sold for home aquariums. It has a fantastic ability to adapt to vagaries of temperature, oxygen content in the water and salinities. Its attractive to home aquariums is the almost chameleonic range of colors it can adopt based on its food intake. Brine shrimp have an elongated body and eleven pairs of legs. That is why they are confused with shrimp and the name.
Brine shrimp are also known as Artemia salina -- which is more of a generic name and several varieties of brine shrimp are in existence. They are arthropods that belong to the class of crustaceans. As zooplankton, one can consider them a major food source for other oceanic life, like Daphnia and Copepods. The brine shrimp lives in salt swamps, man-made evaporation ponds used to obtain salt from the ocean and in salt lakes such as those found in the intermountain desert region of the western United States. Because of their high salt tolerance, they are not victims to many predators. Adult artemia can tolerate salinity of up to 50%. This means that they are literally at home at salinities of salt ponds, which varies from about 2.9% to about 3.5% salt. It can also tolerate salinities of the type in the Great Salt Lake, in northern Utah, which ranges between 25 and 35%. Interestingly, brine shrimp also tolerate and even thrive in a brackish water environment. While they are not susceptible to predators, brine shrimp also do not have a variety to choose from as far as their own nourishment is concerned. This contributes to their hardiness. Like many other primitive aquatic plants this organism is attracted to light, rising to the surface in the daytime, and sinking at night. The positive phototaxis of Artemia keeps it at the same depth as its prey. Phototaxis can be defined as locomotion in response to light. Brine shrimp show a phototaxis, or response to light, that is not fully understood. The adults swim away from light, and the larval forms swim toward it. The shrimp always orient themselves so that their ventral surface faces the light. A pH ranging from 8 to 9 is most optimal for brine shrimp. This is the pH of most of the salt lakes and solar evaporation ponds in which brine shrimp naturally occur.
Environmental factors contribute greatly to the physical characteristics of brine shrimp. Under normal circumstances, they live almost entirely on the photosynthetic green algae, Dunaliella. The oxygen content in the water determines their physical appearance -- which is a direct consequence of what they can consume (depending on oxygen content in the water). With a good oxygen supply, the artemia are a pale pink or yellow. In an abundant supply of green algae, they take on a greenish hue. If there is a low oxygen level in the water with large amounts of organic matter, or a high amount of salinity from evaporation, the artemia will feed on bacteria, detritus and yeast cells, but no algae. It is under these conditions that they produce hemoglobin and look red or orange in color.
If conditions are ideal for growth, reproduction is rapid, and a self-sustaining artemia supply is possible. Many aquarists and hobbyists buy artemia from stores as a brownish powder. This is testament to the resiliency of artemia. Each particulate of the powder is what is known as a cyst. It harbors an independent brine shrimp in a self imposed hibernation. The artemia life cycle begins by the hatching of dormant cysts which are encased embryos that are metabolically inactive. The cysts can remain dormant for many years as long as they are kept dry. When the cysts are placed back into salt water, they are re-hydrated and resume their development. Ideal conditions of temperature are soaking in salt water for about 15 to 20 hours at 25 degrees C. The development proceeds with the cyst wall breaking open, releasing an embryo. Initially the embryo is attached to the wall of the cyst. This suspension in the water resembles a floating parachute. Therefore, it is called the Umbrella stage. At this stage, the embryo is a characteristic of crustacean development. It is called a nauplius. As a generic name, the nauplius is primitive crustacean larva. It is the first larval stage that emerges from the egg and the earliest free-swimming phase in crustacean development. Generally, it has an oval shaped body, three pairs of appendages, and a single median eye near the front. In terms of sheer numbers, the crustacean nauplius is considered by some to be the most abundant type of multi-cellular animal on earth and is an important food source for fish and predatory invertebrates. The metamorphosis then continues. In the first larval stage, the brine fish nauplii are a brownish orange color because of its yolk reserves. It cannot feed due to an underdeveloped feeding apparatus. Approximately 12 hours after hatching, the second larval stage begins. They start filter feeding on particles of various microalgae, bacteria, and detritus. The growth of the nauplii undergoes 15 different and separate molting stages before it reaches adulthood. This stage takes approximately eight days. Adult artemia average about 8mm in length. In perfect growth conditions, they can grow up to 2 centimeters in length. But can reach lengths up to 20mm in the right environment.
The proliferation of brine fish naturally depend naturally on temperature and other conditions. In low salinity and optimal food levels, fertilized females usually produce free swimming nauplii at a rate of up to 75 nauplii per day. She has a brood pouch from which active young are liberated under favorable conditions. They will produce 10-11 broods over an average life cycle of 50 days. Under super ideal conditions, an adult artemia can live as long as three months and produce up to 300 nauplii or cysts every 4 days. Cyst production is induced by conditions of high salinity, and chronic food shortages with high oxygen fluctuations between day and night.
The method of food intake is primitive and reminiscent of the method that amoeba use which is the creation of vacuole. The space between an artemias legs widens as the legs move forward. Water is sucked into this space from below, and small filtering hairs collect particles including food from the incoming stream. On the back stroke, the water is forced out and the food remains in a groove at the base of the legs, this groove has glands that secrete an adhesive material that clumps the food into balls, and micro hairs move the food packages toward the mouth. Artemia are mostly used in aquariums to feed fish. They form a source of nourishment. Newly hatched artemia are high in fats, about 23% of dry weight. By mid juvenile stage, the fat levels have decreased to about 16%, and by the time they are pre-adults the fat levels have decreased to about 7%. But, at the same time, the protein content has risen to replace the fat, from about 45% in a newly hatched artemia to about 63% in an adult.
Brine shrimp's survival in highly saline conditions depends on their ability to pump salts out of themselves and, thus, can keep their internal salt concentrations much lower than those in the water in which they live. This they accomplish by the process of osmosis, where the water leaves the system into the surrounding. Then they must drink their salty medium to replace this osmotic water loss. Of course, this imposes a further burden on their salt-exporting system because the water they drink is very salty. Researchers treated a male brine shrimp as it were a developing photograph. The salt intake capacity probably renders it impervious to the poisonous nature of Silver nitrate. The legs were dyed thus.
The researchers were able to see the legs actively pumping chloride ions out of the body. These "sodium pumps" were powered by certain enzymes. The enzymatic activity increased with proportion to the salt concentration gradient. This is how the brine shrimp evolved to survive in its harsh environments.
One very large home for the shrimp is the Great Salt Lake of Utah, where the water is so salty that fish can't survive. Brine shrimp eggs hatch in the spring, and the shrimp spend the summer reproducing. In autumn and winter, algae food supply dwindles. So is the brine shrimp population. By December, most brine shrimp in Great Salt Lake are dead from the cold but they'll leave behind floating mats of eggs that will hatch next spring. Those tiny eggs are big business. They're harvested for use in the aquaculture industry as feed for prawns and fish. The brine shrimp population has declined dramatically in the last three years. Now millions of migratory…[continue]
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