Brine shrimp nauplii are widely used in aquariculture for feeding early-stage fish and crustacean larvae. The nauplii exhibit two essential qualities for this purpose: they are of an appropriate size to be ingestible, and they move actively in the water column, establishing themselves as targets for young carnivores. Brine shrimp can produce cysts (eggs) under certain conditions and these, since they float, are easily harvestable. The eggs are collected and placed into cold storage for at least three months. This process is called 'Diapause Inactivation' - a process that is similar to hibernation. Following the cold storage period, the eggs are cleaned, washed, and separated. The partially hydrated eggs are disinfected, dried in rotary ovens to about 6% residual moisture, and then vacuum packed. The finished product can then be stored for long periods. When the eggs are placed into saltwater they are re-hydrated and hatch.
Brine shrimp eggs can last for several years as long as they are maintained in a dry condition at all times. Sealed cans can be stored for years at room temperature, but once opened, should be used up within two months. Store opened eggs in an airtight container in the refrigerator or in a cool dry place. If the entire contents of a can will not be used up in two months, it is recommended that the portion that is expected to be unused be placed in a tightly closed container and frozen until needed.
The ease of hatching brine shrimp eggs and the commercial availability of the adult stage has made them a popular food source. Freshly hatched brine shrimp nauplii have a lipid-rich yolk, high in unsaturated fatty acids. Due to this nutritious yolk and small size, brine shrimp nauplii have become the standard food for larval fish in the aquaculture industry. Brine shrimp nauplii emerging from their protective shells are extremely small, mostly less than 500 µm but can differ (400 to 800 µm) according to origin. The smallest is believed to be the San Francisco Bay variety. Another overlooked fact is that fish larvae are thought to take advantage of the nauplius' digestive enzymes, as most fish larvae have a very weak digestive system when being young. There is great variation in nutritional quality, hatching quality, and size of nauplii among commercial sources of brine shrimp eggs.
Brine shrimp nauplii are an excellent live food, not only for larvae but also for adults of the smaller species of rainbowfishes. They can live in freshwater for around 4~5 hours before they die, making them an ideal live food for small rainbowfish larvae. However, they are not suitable as a first food for all rainbowfish larvae; some larvae are so small that they will require microorganisms.
Brine shrimp are a relatively primitive form of aquatic crustacean that occurs naturally in saline waterbodies worldwide. They belong to the subclass Branchiopoda, which is characterised by many pairs of flattened appendages on the thorax, in contrast to other members of the Crustacea that have no more than six pairs. Branchiopoda is an ancient group of primitive crustaceans found today primarily in inland, often temporary, waters such as wet weather ponds and saline lakes. The gills are located on the trunk appendages, hence the name Branchiopoda (= gill foot). The lack of a true carapace places them in the suborder Anostraca, and further in the family Artemiidae. The Anostraca are branchiopods in which there is no carapace (anostraca = without shell) and are similar in many features to the ancestral crustaceans. The group is small and includes the fairy shrimps and brine shrimps. Probably the most distinctive feature of Artemia is the compressed, triangular, and blade-shaped distal segment of the second antenna of the male. In the male the antennae are transformed into muscular claspers used to secure the female during copulation. The mature adult is 8 to 10 mm long with a stalked lateral eye, sensorial antennulae, a linear digestive tract, and 11 pairs of thoracopods.
Australian saline lakes harbour a rich diversity of endemic brine shrimps (Parartemia), which, like Artemia, can produce cysts from which nauplii hatch, but under quite different limnological conditions. Their economic and scientific values remain almost totally unexplored. Australia also has a freshwater cousin of the brine shrimp (Branchinella), which occurs in temporary fresh waters (pools, ditches, rock-pools, and ponds).
The environmental conditions under which brine shrimp live are highly variable. The salinity can exceed 300‰ (parts per thousand) where most other life cannot survive. Advantaged by the absence of predators and food competitors in such places, brine shrimp develop very dense populations. Although not a marine species, they sometimes occur in bays and lagoons. They are more commonly found in highly saline lakes, such as the Great Salt Lake, Utah where the shoreline may become ringed with brown layers of accumulated brine shrimp eggs.
The development of brine shrimp is influenced by many factors and the tolerance of these factors is strain dependent. Optimum temperature for most strains ranges between 25 and 35ºC but strains have been reported thriving at 40°C. Most geographical strains do not survive temperatures below 6°C except as eggs. These eggs are tolerant of temperatures from far below 0°C to near the boiling point of water.
Although brine shrimp can survive and reproduce under a wide range of salinity, they are seldom found in nature in salinities below 45‰ or above 200‰. The pH tolerance varies from neutral to highly alkaline but the eggs will hatch best at a pH of 7.5 to 8.5. Many predators including zooplankton that populate natural salt waters, fish, several insect groups (odonates, hemipterans and beetles), and birds feed on brine shrimp in situations where they can tolerate the conditions.
Copulation is initiated when the male grasps the female with its modified antennae. At low salinities (<85‰) and optimal food levels, fertilised females usually produce free swimming nauplii (ovoviviparous reproduction) at a rate of up to 75 nauplii per day. They may produce 10~11 broods over an average life cycle of 50 days. Under ideal conditions adult brine shrimp survive for several months and produce up to 300 nauplii every 4 days. Cyst production (oviparous reproduction) is considered to be induced by high salinity, under conditions of high eutrophication (large O2 fluctuations between day and night) and chronic food shortages. At high salinities (>150‰) and low oxygen concentrations, the embryos develop to the gastrula stage. They then become surrounded by a thick shell and enter dormancy (diapause). Females can release up to 75 cysts per day which float in the highly saline water (eggs from Mono Lake in California sink). The floating cysts are eventually blown ashore where they accumulate in large masses and dry.
Development is resumed when the cysts are re-hydrated and the life cycle is begun again. After several hours the outer membrane bursts and the embryo emerges still encased in the hatching membrane. Soon the hatching membrane is ruptured and the free-swimming nauplius is born. The first instar is brownish-orange coloured and has three pairs of appendages. The larva grows through about 15 moults and becomes differentiated into male or female after the tenth moult.
Brine shrimp are typically filter feeders that consume organic detritus, microscopic algae, and bacteria. Blooms of microscopic algae are favourite habitats, and large populations develop in such areas where they feed on the algae and heterotrophic bacteria that are produced by these blooms.
The standard procedure for hatching brine shrimp nauplii is to incubate the eggs for 24~48 hours in a saltwater solution and then separate the nauplii from the unhatched eggs and shells. I use a 2-litre wide-mouthed glass jar filled with tap water. To this I add 10 to 20 grams (2 to 4 level measured teaspoons) of cooking salt and a pinch (¼ level teaspoon) of Sodium bicarbonate.
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| Brine shrimp after settling period |
Siphoning Brine shrimp |
Brine shrimp eggs have been shown to hatch out at salinities ranging from 5 to 35‰ (parts per thousand). However, research has shown that better hatching results have been achieved at the lower range. During the hatching process, the eggs absorb water through the shell by osmosis. When the osmotic pressure within the egg is great enough, the shell then bursts, freeing the larval brine shrimp. At higher salinities, the osmotic pressure outside the egg is higher than within the egg, lengthening the time for hatching. However, if you are having problems with poor hatch rates then experiment with different salt levels as I have found that you can get better results using different salinity levels.
The pH for the hatching solution may range from 7.5 to 8.5. A pH above 9.5 tends to be too alkaline, while a pH below 6.5 results in a dramatic decrease in the hatching results. Hatching time varies with incubation temperature and the geographic strain of brine shrimp used. The temperature for optimal hatching rate and high hatching efficiency is considered to be 27~30° Celsius. However, at least 90% of premium grade eggs should hatch within an 18-hour period in a temperature range of 25~32° Celsius. Lower temperatures will cause the eggs to hatch at a slower rate. The air temperature of my fishroom governs the temperature in my case. During summer, I harvest the shrimp after 24 hours, wintertime 48 hours, and spring/autumn 36 hours. I live in a sub-tropical climate and my fishroom rarely drops below 20°C during winter, but in summer it can reach 30 to 35°C.
The recommended hatching density of eggs should not exceed 5 grams per litre of water. Constant aeration should be provided by an airline, without an airstone, inserted to reach the bottom of the jar. Aeration is essential for two reasons - the maintenance of dissolved oxygen levels, and keeping the eggs suspended in solution. Adjust the air supply so that moderate aeration occurs. Too little aeration will result in low levels of dissolved oxygen while too much aeration will cause the cysts to stick to the upper jar out of the water. These conditions will significantly affect the hatch rate. After the incubation period, turn off the aeration and allow the contents to settle for about 5 to 10 minutes. A distinct separation will occur, the hatched eggshells will float to the surface, and the unhatched eggs will sink to the bottom.
Most of the newly hatched nauplii will accumulate just above the unhatched eggs on the bottom. Siphon the shrimp into a fine mesh net (<150 µm) through a length of airline tubing, which has a short rigid extension (the depth of the jar) on the intake end. This makes it possible to position and siphon very accurately. This separation step is necessary, however, because small fry cannot digest unhatched eggs and shells, which can cause mortality if consumed. After rinsing the nauplii in a gentle stream of freshwater, which will remove any waste or salt residue, the nauplii can be fed to the fish. It is important to collect the nauplii quickly, because after 10 minutes or so, the oxygen levels of the water begin to drop quickly and the nauplii will begin to show signs of distress and die.
Discard the remaining contents of the hatching jar and wash with hot soap and water, rinsing well before use. The net should also be rinsed. Prepare fresh salt water for each new hatch. To have a fresh supply of brine shrimp daily, at least two hatching containers should be used; so that newly-hatched shrimp can be harvested daily.
Artemia nauplii are most nutritious while they contain the yolk sac and should be fed as soon as possible after hatching. Artemia nauplii in their first stage of development can not take up food and thus consumes its own food reserves. At 28°C, the freshly-hatched Artemia nauplii develop into the second larval stage within a matter of hours. It is important to feed first-instar nauplii to the fish rather than second-instar meta-nauplii which have already consumed 25 to 30% of their food reserves within 24 hours after hatching. Moreover, instar II Artemia are less visible as they are transparent, are larger and swim faster than first instar larvae, and as a result consequently are less accessible as a prey. Furthermore they contain lower amounts of free amino acids.
Moulting of the Artemia nauplii to the second instar stage may be avoided by storing the freshly-hatched nauplii at a temperature below 10°C. Only slight aeration is needed in order to prevent the nauplii from accumulating at the bottom of the container where they would suffocate. In this way nauplii can be stored for periods up to more than 24 hours without significant mortalities. This technique allows not only a constant supply of high quality nauplii but also more frequent feeding for freshwater fish larvae.
© Copyright Adrian R. Tappin
Updated December, 2009.
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