Some scientific facts from the book: "Biology of Aquatic Organisms: Artemia - Basic and Applied Biology"
Edited by: Th.J.Abatzopoulos, J.A.Beardmore, J.S.Clegg and P.Sorgeloos BUY THIS BOOK - IT'S WELL WORTH THE MONEY!!!
How long are Artemia females pregnant (Sea Monkey pregnancy):
5 days after oocyte fertilization the encysted embryos
or the nauplii are released from the female egg sac.
Nauplii emergence is less clear, but it is inhibited
by heavy metals, bicarbonate deficiency and metabolic
perturbation.
Fertilization in Artemia occurs within an hour after copulation,
and before this event spermatozoa reside in the median area of
the ovisac, which functions temporarily as a receptaculum seminis.
Not all encysted embryos oviparously produced enter diapause,
sometimes nauplii emerge from some cysts without dehydration,
which is needed for complete development of the embryos. Those
cysts are surrounded by a much thinner shell
than those which enter diapause.
The encysted gastrual embryo ('cyst') is the most resistant of
all animal life history stages to extremes of environmental stress,
while the living animals are among the best osmoregulators in the
animal kingdom.
The sugar disaccharide trehalose is present in big amounts
in Artemia cysts, making up about 15% of their dried weight.
It is suggested that that trehalose protects cell membranes and
proteins against the destructive effects of dehydration.
Hydrated Artemia cysts survived a full year of continuous anoxia
without significant reduction in hatching, and only a modest
reduction after the second year. About 60% survived 4 years of
anoxia and almost 10% survived more than 6 years; indeed, almost
7 years of continuous anoxia were required to reduce hatching to zero.
Dried cysts survive exposure to 2.2K, and have been reported to
survive an hour or so at 103C with little reduction in hatching.
Artemia franciscana has the greatest temperature tolerance
range of any Artemia species
In an experiment, cysts were adhered to a static substrate and
over 75% emerged upwards and only 1% downward. The direction of
light and point of cyst adhesion had no effect on these results.
Artemia cysts in NASA's Space Shuttle Discovery emerged in random
directions, while experiments with large gravity (hypergravity 73g(!))
on Earth (1g) increased the proportion of upward-emerging cysts to 91%.
A scientist suggested that the significance of these results is
for the need for cysts in lake sediments to emerge in the direction
of the water column.
Swimming, feeding and other vital activities are seriously disturbed
if the dissolved oxygen level falls below about 2 ml O2/l at seawater
salinity. Below 1.5 ml O2/l, respiration falls drastically and the
organism stops moving and relies on anaerobic metabolic pathways for
survival.
Mature Artemia can withstand salinities as high as 340 g/l,
more than 10 times the salinity of sea water, and a very low
dissolved oxygen level as low as 1.5-2.0 ml/l, being less than
half the 5 ml/l typical of surface seawater.
The relatives of Artemia, Parartemia in Australia is about twice
the size or Artemia. Parartemia cysts sink rather than float,
which might be an explanation for the isolation of different
species in different Australian salt lakes.
Anostraca, where the Artemia belong to, first appeared about 400
million years ago and from the scanty fossil record it appears
that fairy shrimp and brine shrimp were among these early crustaceans.
They changed very little in their morphology (and probably physiology
and biochemistry as well) for 100s of million years.
Artemia is widely distributed on the five continents in many salt
lakes, coastal lagoons, and solar saltworks.
500 Artemia sites worldwide are known
No natural Artemia populations are found in humid climates and 97%
of the biotopes are located in areas where yearly
evaporation exceeds yearly precipitation, that means that lakes
evaproate on a regular basis, before they are filled up with rain
water again.
No best salinity can be defined for Artemia, but for physiological
reasons a optimum must be situated towards the lower end of the
salinity range. Higher salinity requires higher energy cost for
osmoregulation.
The optimal temperature for Artemia is in the range of 25-30C.
The ametabolic dehydrated cysts resist a much wider
temperature range, which never occurs in nature: the
minimum being the absolute zero (-273C) and the maximum close
to 100C for short exposure time.
San Francisco Bay nauplii die within a few days in the carbonated
water of Mono Lake.
Artemia reproduce sexually in the Americas, while they reproduce
parthenogenetic and bisexual in the rest of the world (including Australia).
In Sardinia both sexual and parthenogenetic populations have been
found only a few kilometers apart, the parthenogenetic populations
being associated with a commercial coastal solar saltworks, and
the sexual population in a natural saltpans located a few
kilometers inland. Parthenogenetic strains have more haemoglobin
than sexual species, which might be advantageous at high salt concentration.
Artemia and Parartemia diverged at minimum 85 million years ago,
a date coinciding with the geological isolation of Australia in the
late Mesozoic.
Parartemia has limited adaption to low oxygen levels.
The max. size of Parartemia is 22mm, significantly larger than Artemia.
Parartemia is adapted as a sediment eater, while Artemia is a filter
feeder, filtering planktonic algae.
Names for Artemia in Australia (scientifically not accepted): Artemia
proxima, Artemia australis, Artemia westraliensis
Parartemia species: Parartemia zietziana, Parartemia minuta
Current Artemia species very likely to have diverged from an
ancestral form living in the Mediterranean area some 5.5 million years
ago.
Artemia has been known to and used locally by humans probably for
centuries. Hence its many popular names such as "brine shrimp",
"Fezzan worm", "Bahar-el-dud", and others.
Some facts from www.fao.org
Tolerance to environmental factors
Nauplii
Growth optimal at 28°C and 35 ppt
Growth slows at pH lower than 7
Respiratory metabolism shows a reversible stop at 5-8°C
Death occurs at 0°C and 37-38°C
No mortality occurs when Instar I larvae, hatched in 30 ppt are transferred to 90-110 ppt immediately.
Can be transferred from 30°C to 4°C - activity stops suddenly but can be reactivated by increasing the temperature again
Adults
When put in freshwater, adults for 2-3 hours
Max. salinity for most strains is at 200 ppt
Increasing salinity with 10 ppt changes in 4 hour intervals is very well tolerated
Morphology and general appearance of adults change within different salinities
The higher the salinity the smaller the claspers of the male Artemia.
In high salinities, the body becomes longer and thinner than in low salinities.
At pH lower than 7, the general appearance of Artemia grows worse
pH 8-8.5 seems to be optimal
At 28°C growth is optimal and temperature higher than 36-37°C are lethal
Nauplii as well as adults survive a sudden fluctuation from 28-30°C to 0-4°C and vice versa
At temperatures of 0-4°C most motion activity stops.
Low oxygen concentrations are more harmful for nauplii in the first stages than for later stages and adults,
since then gills are formed.
