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Brine shrimp

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Brine shrimp belong to the genus Artemia, which is a group of aquatic crustaceans.

Brine shrimp cyst
Brine shrimp cyst

They are the only genus within the family Artemiidae. These animals are famous for living in environments that most other creatures cannot survive. They typically inhabit inland saltwater lakes, though they are sometimes found in oceans. Most predators, such as fish, cannot live in these waters. This is because brine shrimp can tolerate very high salinity levels. They can survive in water with salt concentrations as high as 25%. This ability allows them to occupy a unique ecological niche.

An adult brine shrimp has a body divided into three main parts: the head, thorax, and abdomen. Their bodies are covered by a thin, flexible exoskeleton made of chitin. This outer shell is shed periodically through a process called moult. In female brine shrimp, a moult occurs before every ovulation. The body usually consists of 19 segments. The first 11 segments have pairs of appendages used for movement and breathing. The next two segments often carry the reproductive organs. The final segments lead to the tail. Adult males are usually about 4 mm long, while females are slightly larger at 6 mm.

Artemia monica
Artemia monica

Brine shrimp have fascinating ways of moving and sensing their world. They use rhythmic beating of their appendages in pairs to swim. Respiration happens on the surface of their legs through feather-like plates called lamellar epipodites. They also possess two different types of eyes. Adults have two widely separated compound eyes mounted on flexible stalks. These are their main optical sense organs. However, the larvae, known as nauplii, use a different eye. This is called a naupliar eye, or median eye, located in the center of the head. Interestingly, many of their functions are not controlled by a central brain. Instead, local nervous system ganglia regulate swimming, digestion, and reproduction.

One of the most remarkable survival mechanisms is cryptobiosis. This term means "hidden life." When conditions become extreme, such as low oxygen or very high salinity, females produce eggs with a protective brown coating called a chorion. These eggs are known as cysts. In this state, the cysts are metabolically inactive. They can remain in total stasis for two years in dry, oxygen-free conditions. They can even survive temperatures below freezing or near boiling.

Brine shrimp cyst
Brine shrimp cyst

This resilience makes them ideal for space aquaculture. Scientists have even flown cysts on Apollo 16 and Apollo 17 missions to the Moon. These experiments tested how cosmic radiation affects life.

Brine shrimp also exhibit unique methods of reproduction. Some populations use parthenogenesis, which is a form of reproduction without fertilization. A specific type is called thelytoky, where female individuals develop from unfertilized eggs. One method, known as automixis, involves the combination of two haploid products from the same meiosis. Specifically, some species use central fusion to form a diploid zygote. This process helps maintain heterozygosity, which is the presence of different genetic versions. This helps minimize inbreeding depression in these populations.

Central fusion and terminal fusion automixis
Central fusion and terminal fusion automixis

Because of their life cycle, brine shrimp are vital to aquaculture. This is the farming of aquatic animals. Cysts can be stored indefinitely and hatched on demand. This provides a convenient live food source for larval fish and crustaceans. The hatched larvae, or nauplii, are highly nutritious. Many cysts are harvested from the Great Salt Lake in Utah to be marketed worldwide.

Artemia breeding ponds
Artemia breeding ponds

They are also used in biological toxicity assays. Because millions of them can be easily reared, they serve as model organisms to test the effects of environmental pollutants. This provides an alternative to testing chemicals on mammals.

Despite their abundance, some brine shrimp populations face significant threats. Habitat loss and introduced species can cause local declines. For example, A. franciscana has been introduced to many areas and can outcompete native species like A. salina. In Lake Urmia, Iran, the species A. urmiana has declined due to drought. In California, the species A. monica lives in Mono Lake. There were concerns that rising salinity and pH levels from water diversion might endanger them. However, after a review of the situation, they were not added to the endangered species list in 1995. Scientists continue to study these resilient creatures to understand their unique genetic adaptations to extreme environments.

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🖼️ Images & Media (4)
File:Brine shrimp cyst.jpg
Brine shrimp cyst.jpg
File:Central fusion and terminal fusion automixis.svg
Central fusion and terminal fusion automixis.svg
File:Artemia breeding ponds.jpg
Artemia breeding ponds.jpg
File:Artemia monica.jpg
Artemia monica.jpg
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