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Feeding: Artemia

The common brine shrimp (artemia) is in the phylum Arthropoda, class Crustacea. Artemia are closely related to zooplankton like Copepods and Daphnia, which are also used for live food in the aquarium. 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. Artemia cysts are best stored in a tightly sealed container in a cool, dry environment. The refrigerator is usually best.

After 15 to 20 hours at 25 degrees C (77 degrees F) the cyst bursts and the embryo leaves the shell. For the first few hours, the embryo hangs beneath the cyst shell, still enclosed in a hatching membrane. This is called the Umbrella stage, during this stage the nauplius completes its development and emerges as a free swimming nauplii. In the first larval stage, the nauplii is a brownish orange color because of its yolk reserves, newly hatched artemia do not feed because their mouth and anus are not fully developed. Approximately 12 hours after hatch they molt into the second larval stage and they start filter feeding on particles of various microalgae, bacteria, and detritus.

The nauplii will grow and progress through 15 molts before reaching adulthood in about 8 days. Adult artemia average about 8mm long, but can reach lengths up to 20mm in the right environment. An adult is a 20 times increase in length, and a 500 times increase in biomass from the nauplli stage.

In low salinity and optimal food levels, fertilized females usually produce free swimming nauplii at a rate of up to 75 nauplii per day. 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.

Adults can tolerate brief exposures to temperatures as extreme as -18 to 40 degrees C (0-104 degrees F) Optimal temperature for cyst hatching and adult grow out is 25-30 degrees C (77-86 degrees F), but there are differences between strains, San Francisco bay strain is 22 degrees C as compared to 30 degrees C for Great Salt lake.

Artemia prefer a salinity of 30-35 ppt (1.0222-1.0260 density) and can live in fresh water for about 5 hours before they die. Caution should be used to not over feed in a fresh water aquarium because of the rapid decomposition of the dead. Many fresh water fish will tolerate and even thrive in a brackish water environment of 1-5 ppt easily, so it is possible to add saltwater to the tank and extend the survival of the artemia if required.

Other variables of importance are pH, light and oxygen. A ph of 8-9 is best; pH less than 5 and greater than 10 will kill the culture. the pH can be increased with baking soda, and lowered with muriatic acid. A minimum amount of light is necessary for hatching and may be beneficial for adult grow out. A standard grow lite bulb available in an aquarium supply is adequate.

Most important is the level of oxygen in the water, as this dictates what the artemia will consume. With a good oxygen supply, the artemia are a pale pink or yellow, or if they are heavily feeding on microalgae they will look green in color. In this ideal condition growth and reproduction is rapid, and a self-sustaining artemia supply is possible. 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 this environment remains they will start producing resting cysts, and the colony may crash. It is very important to have a vigorous air supply in the tank for two reasons, one is to keep the available food supply in suspension where it can be filtered out, and the other is to promote a good oxygen supply in the system. (in other words - a boiling cauldron is fine)

Written by Kai Schumann