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Artemia questions
>"contaminated green water" cultures
>The only cure I've found for this so far is to have multiple >cultures and
>discard any contaminated with this kind of algae, >washing all equipment
>from that culture in a strong bleach solution.
Macro-algae are so much more efficient in taking up nutrients from the water
that the micro-algae just don't stand a chance once contamination has
occurred. Furthermore, if you have blue-gree algae present, they will
outcompete micro-algae because they can carry out nitrogen fixation.
>I would have thought that the brine shrimp could eat the smaller >rotifers.
>They seem so small and they seem to disappear when added >to a hatching jar
>of brine shrimp eggs. Any ideas where they go?
Brachionus plicatilis for instance is barely visible in the water except
when you have a dense culture (e.g. a couple of hundreds of animals per
milliliter) going; and then you see "turbid water with moving dots".
Although barely visible, the animals still have a length from 150 micrometer
for B. plicatilis rotundiformis, upto 220 micrometer for B. plicatilis
typicus. During culturing, I have noticed on plenty of occasions that the
length of the rotifers kept on increasing generation after generation ...
until a certain limit of course. I have no explanation yet for why this
happens.
Maximum size of particles supposed to be ingested by adult Artemia hoovers
around 50 micrometer, so rotifers like Brachionus are just way too big.
Also, do not forget that Artemia are filter-feeders just like rotifers are
and that they swim randomly through the water, supposedly "guided" by
phototaxis, chemotaxis and temperature preferences. Males use their modified
antennae only for grasping females during copulation, never for feeding. The
fine hairs on the thoracopods filters debris, bacteria and algae out of the
water which moves through these hairs as the thoracopods are used for water
displacement. These hairs then move the filtered particles to a medioventral
groove in which the beating of well-coordinated cilia transport the food to
the mouth. Therefore, other zooplankton is too big (and or fast) to be eaten
by Artemia.
>I have also heard the theory that the small amount of salt that may >be
>still inside the brine shrimp helps to swell the digested brine >shrimp
>with absorbed water and make it possible for the fry to eat a >larger meal
>the next time. Is there any truth to that or is it an >old fishwife tale?
Hmmm ... coincidence that you mention this. A couple of weeks ago I was
checking the level of enrichment of brine shrimp and I noticed salt crystals
in the brine shrimp gut. I never saw this before! Might it be that salt was
crystallising in the gut because of the heat provided by the lamp under the
microscope? My "gutfeeling" tells me that the water should not be able to
evaporate so quickly from the gut. So would the brine shrimp have ingested
some minuscule salt crystals? Possible of course, but in the salinity ranges
we harvest the shrimp from salt crystals are not normally found. Gypsum
crystallises on the bottom of some of these ponds yes, but not salt. That
only happens in the crystallising ponds where no brine shrimp are present.
So would these crystals, if they are present, enlarge the stomach of some
fry? I don't think so, as there always is some water present in the
digestive system. Water actually moves to the other tissues due to the
higher osmotic pressure in these tissues. So if you increase the osmotic
pressure in the gut, you just lower the osmotic pressure. But the salt
crystals might exceed the osmotic pressure, this time directing water flow
to the gut hereby enlarging the gut. Let me talk about this with some of my
colleagues in aquaculture.
>How could this be experimentally determined?
Good question. Maybe we can do this later but with the techniques available
now? I seriously doubt it. We even don't know which bacteria are actually
present and beneficial in fry due to difficulties related to their small
size! How to sample bacteria from the gut of fish fry?
>is it ok to use the brine solution in which previously brine shrimp >raised
>to adulthood or I have to make new solution every time for >raising baby
>brineshrimp to adult brineshrimp
Would advise against it. I for myself have noticed that by using
"old" water, e.g. 10 liters of diluted brine which was left in the lab for a
week without aeration, I succeeded in seriously decreasing a couple of
hatches. Hatching the eggs in new medium overcame the bad hatch. Now,
aquarium water isn't old water of course, but you might start with hatching
the eggs in bacteria-loaded water which might increase the biological oxygen
demand in the cone, hereby effectively decreasing the hatch.
>let me double check an assumption I've made. Once the can is miss->handles,
>miss-stored or just plain being used (without cold >storage), it's not
>possible to reverse the shelf life by storing it >in the fridge.
Correct, you can not reverse the shell life of cysts gone bad, but you might
save cysts in which the embryo hasn't consumed all energy yet (see following
paragraph), hereby extending the shelf life of these cysts.
>Once the diapause has been broken, then there is a limited time >frame for
>cyst viability. Is that correct?
Yes. Once diapause has been broken the cysts are just awaiting the right
fysical parameters in order to hatch. We should keep them dry in order to
limit metabolism. When moisture content of cysts is kept below 10%,
metabolism is not measurable. We don't exactly know if it stops completely,
but it is darn low as it is not measurable in the lab. The same goes for
temperature: at low temperatures there barely is any metabolism going on.
When these conditions aren't met anymore, the embryo in the cyst can take up
metabolization again, albeit still at a slow rate. But after years and
years, the embryo has consumed so much energy which was stored in the cyst,
that it doesn't have enough energy anymore to break through the membranes
when the shell bursts (the latter through osmotic pressure building up in
the cyst).
I guess that this contribution will be long enough for this time!
Steve Geerts
Biologist San Francisco Bay Brand
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