Brine Shrimp
Brine shrimp are a relatively primitive form of aquatic crustacean that occurs naturally in saline waterbodies worldwide. Their taxonomic status has long been controversial because there is considerable morphological variability across their geographical range. The present consensus is that there is a single cosmopolitan species, Artemia salina, which has numerous intergrading physiological and morphological varieties.
Brine shrimp 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 salina 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.
Brine shrimp are a common food source used for both larval and adult fishes. The ease of hatching eggs and the commercial availability of the adult stage has made it a popular food source. Brine shrimp nauplii emerging from their protective shells are extremely small, mostly less than 500 µm but can differ according to origin. The smallest is believed to be the San Francisco Bay variety and the largest was found to be a stain from China.
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. Another overlooked fact is that fish fry are thought to take advantage of the nauplius' digestive enzymes, as most fish fry have a very weak digestive system when being so young.
Brine shrimp nauplii are an excellent live food, not only for fry but also for adults of the smaller species of rainbowfishes. However, they are not suitable as a first food for all rainbowfish fry; some fry are so small that they will require micro organisms. Brine shrimp nauplii can live in freshwater for around 4-5 hours before they die, making them an ideal live food for small rainbowfish fry.
Alvin Seale, the Superintendent of the Steinhart Aquarium, USA, first reported the suitability of brine shrimp nauplii as a source for larval fish in 1933. However, it wasn't until the late 1970s that a continuous supply of eggs was available. At that time, the major supply of eggs occurred in the United States, mainly from San Francisco Bay and the Great Salt Lakes, Utah. Commercial brine shrimp farms have now been established in many parts of the world, and are commonly introduced into evaporation ponds used for the commercial production of salt.
Australia has an endemic species of brine shrimp (Parartemia), which occur in inland saline lakes. There are about a dozen known species and they produce eggs, from which the nauplius larvae hatch, similar to Artemia. Their economic and scientific values remain almost totally unexplored. Artemia salina has been introduced into many coastal, solar salt fields in Australia and has been found in at least one natural salt lake well inland. 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 (cysts).
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 35°C 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.
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.
Copulation is initiated when the male grasps the female with its modified antennae. The fertilised eggs develop either into free-swimming nauplii, or they are surrounded by a thick shell and deposited as cysts, which are in diapause. Most strains of brine shrimp produce eggs that float (eggs from the Mono Lake, California sink). These eggs remain in diapause as long as they are kept dry or under anaerobic conditions.
Upon hydration, the embryo in the egg becomes activated. 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.
Female brine shrimp produce eggs during periods of high salinity, shortage of suitable food, low oxygen levels and continuing high temperature extremes (during optimal conditions they usually produce free swimming nauplii). The eggs are collected and are placed into deep, 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 be stored for as long as 2 years or more. When the eggs are placed into saltwater they are re-hydrated and hatch.
Brine shrimp eggs should be 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. Brine shrimp are sometimes marketed under the improbable name of "sea monkeys".
Hatching
In recent years, several nutritional enhancement techniques have been developed to improve the nutritional value of brine shrimp by maintaining them for several days in a nutrient-rich medium. Obviously, the time and effort involved in nutritionally enhancing brine shrimp would not be worthwhile for the average aquarist. However, for the serious aquarist with an extensive breeding program, nutritionally enhanced brine shrimp may well be worth the effort. Every aquarist should be familiar with the brine shrimp as they are easily cultured. The standard procedure for hatching 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 will outline my method for hatching brine shrimp:
Brine shrimp after settling period Siphoning Brine shrimp
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 of Sodium bicarbonate. Brine shrimp eggs have been shown to hatch out at salinities ranging from 5 to 35 parts per thousand (ppt). 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. If you are having problems with poor hatch rates then experiment with different salt levels as I have found that different Brands require different salinity levels.
The pH for the hatching solution may range from 7.5 to 8.5. A pH above 8.5 tends to be too alkaline, while a pH below 6.5 results in a dramatic decrease in the hatching results. The optimum hatching temperature is considered to be 28°C. From 25 to 32°C at least 90% of premium grade eggs should hatch within an 18 hour period. Lower temperatures will cause the eggs to hatch at a slower rate. The temperature in my case is governed by the air temperature of my fish room. During summer, I harvest the shrimp after 24 hours, winter time 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. Proper aeration is essential for two reasons - the maintenance of dissolved oxygen levels, and keeping the eggs suspended in solution. Too little aeration will result in low levels of dissolved oxygen, while too much aeration causes the build-up of foam on the surface of the water. Eggs that become caught up in this foam will not hatch.
After the incubation period, I turn off the aeration and allow the contents to settle for about 5 to 10 minutes. A distinct separation will occur, the hatched egg shells 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. I then siphon the shrimp into a fine mesh net through a length of air-line 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. Careful siphoning can be time consuming however, this is necessary because unhatched eggs and shells cannot be digested and may become caught in the stomach of small fish, thus leading to mortalities.
I then rinse the nauplii in a gentle stream of freshwater, which removes any waste products and salt residue. The freshly hatched nauplii are then fed to the fish. The jar is then emptied, rinsed, refilled with tap water and the procedure is started all over again. The net should also be rinsed. 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.