FILTRATION OF SHRIMP HATCHERY INTAKE WATER
From: npesantes@hotmail.com
To: shrimp@egroups.com
Sent: 26 January 2001
QUESTION:
If you were going to build a larvae laboratory in
Ecuador, would you do it without the water filters for larviculture?
Supposing you build it, would you consider that
larvae produced in this laboratory, thanks to the work with direct water,
were of a better quality than those produced in traditional systems?
Nelson Pesantes
E-mail: npesantes@hotmail.com
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COMMENTS 1 :
Of course the larvae will be fitter and better
adapted to enter into the
wild environment of your ponds. In my opinion too many hatcheries are built
and run as if they are hospitals. This would be OK if the on growing is also
bio-secure. However in reality in Ecuador almost all hatcheries supply
standard semi-intensive farms and so it means that a certain percentage of
larvae will be compromised when facing the new challenges of non bio-secure
grow-out ponds. The trend seems to be towards bio-secure farms (pushed by
foreign experts and equipment sellers who would probably love this to
happen?) Alternatively, one could consider un-bio-securing (?) the
hatcheries. This could mean exposing the larvae to inoculation by changing
the 'perceived' required standards of control that are taken for granted in
Ecuadorian hatcheries and forcing the nauplii to be grown more organically.
A high tech hatchery nowadays adapted for Ecuadorian semi-intensive farmers
might be one that more closely emulates the natural conditions rather than
one that fills itself up with high tech gadgets and systems.
The hatchery I built in Mexico had only beach sand filtration for
larviculture (from a beach intake at about 100 microns). It was less
filtered (on purpose from experience) than the hatchery I had prior in
Ecuador. We even had small jelly fish growing in the tanks with the PL10's !
Survival in Mexico was only 30% from nauplii to PL10 but those larvae had
passed through the survival of the fittest trial. The shrimp did real well
in the ponds. We also supplied the USNMFS with their original SPF strain and
high health concept larvae in the late 1980's. Whether this practise was
sustainable I never found out....perhaps there are other people out there
that still have 'open' larviculture systems?
Patrick Wood
E-mail: patjwood@hotmail.com
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COMMENTS
2 :
In the present conditions of contamination and
proliferation of diseases, every measure to reduce the risk counts. On the
other hand, the quality of the larvae depends on many other factors and it
would be necessary to analyze them to be able to determine the quality of
the commercialized product, but the fact of not counting on filters for
larviculture indicates that there is a probability of contamination by not
detected pathological agents in the laboratory.
Fabian Jijon
E-mail: fjijon@ecua.net.ec
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COMMENTS
3 :
I agree on Patrick comments, in fact when we stocked
PL coming from low survival larviculture tanks, we have been able to see
improved survival and growth in ponds, when we started to work with
juveniles instead of pl direct
stocking we started to see improvement in survivals in ponds, this once we
had wssv in Ecuador; this is
how the raceway phase came up, where you can get rid of weaker animals and
boost stronger ones.
Had we done this before, we probably would have had
even higher yields before wssv.
This may be why we didn’t get 80 or 90 % survival before, when 40 to 50
was usual.
We end up with a higher pl or juvenile cost but a more profitable grow-out yield
The concept of adding the raceway phase to me has been already proven in
Ecuador.
I believe in a future industry working hard on
incorporating the juvenile production phase to obtain higher yields in the
grow-out stage. A plus to this will be the domestication and genetics
program underway in Ecuador, which has started also to show positive initial
results with survivals which have reached above 50 %, and not only once but
several times.
From nauplii to juveniles that we stock in ponds a
lot must be lost, in grow-out phase 7 or 8/m² will work, and 3.5
or 4 crops a year will make Ecuador come back.
Jorge Cordova
E-mail: cordova@ecua.net.ec
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COMMENTS 4 :
Could you elaborate a bit on the technical parameters
of the raceway system you have for production of juveniles? I think this
issue of direct stocking versus nurseries/raceways etc. for juvenile
production is a rather interesting discussion point and several readers not
only in Ecuador can benefit from your experience.
What about mortality rates after stocking juveniles due to handling from the
transfer to the grow-out ponds? How do you handle the transfer process?
Mario Pedini
Aquaculture and Fisheries Development Officer
FAO Investment Center
E-mail: mario.pedini@FAO.org
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COMMENTS 5 :
I believe that this topic is perhaps better answered
from a biological
point of view instead of a historial or specifically economic side.
If we consider the first pelagic stages of
larvae (Zoea through
Mysis), these stages occur in the open ocean and it is not until the PL
stages that the larvae migrate in towards the coastal areas showing a more
benthic behavior.
The densities that hatcheries work at (to make them
economically
viable) are extremely high compared with a natural situation, thus requiring
emphasis on water treatment and preparation.
A direct intake is using coastal water which is of
considerably lower
quality than oceanic water (greater organic load) and I feel that this would
not be in any way beneficial to pelagic larval stages. I do think that the
use of direct coastal water would be of great benefit once the larvae reach
their benthic phase in life (PL onwards) and the weeding out of the weaker
ones could start at this stage and continue onto the raceways in the farms.
This could prove more economical than starting off with direct intakes since
your losses in Zoea/Mysis would be high, due to inappropriate conditions.
With good survivals to PL you would be starting of with more to play with.
Andrew C. Watkins
E-mail: andy@aqualider.com.br
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COMMENTS 6 :
But has anyone out there actually done this from PL
onwards or does anyone do it on a commercial ongoing basis ?
If it is practised anywhere, are there results that can be shared?
Patrick Wood
E-mail: patjwood@hotmail.com
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COMMENTS 7 :
In summary, if you stock pl's in your pond with a good survival from tanks, you will
increase the possibilities to reach an improved survival.
Gabriel Rivera
E-mail : griveralo@yahoo.com
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COMMENTS 8 :
Mortalities after transfer do occur but they don’t
seem to be so aggressive as when PL are stocked directly if we associated to
wssv. In the case of
mortalities produced by handling of the animals they should be minimal, if
the process is performed with care. The raceways are located at the farm
site, so no long periods of transportation are involved. Transportation is
done in tanks, an oxygen supply is needed. For example I have moved 200,000
animals, average 50 pieces per gram, in a tank in a boat for 45 minutes in
400 liters of water from the raceway to the pond without too much of a
trouble. During the transportation period water was exchanged with buckets,
probably
some 20 to 30 %. Survival in pond was 59 %, stocking density was 2/m² in
the pond. This occurred during the dry season colder months.
Bigger and smaller juveniles should be transported in numbers or should I
say biomasses that vary accordingly. Transportation time should also be
considerred and oxygen addition is key factor.
The use of the raceway phase also has a positive social impact in a country
like ours since new jobs are provided at the farms.
Jorge Cordova
E-mail: cordova@ecua.net.ec
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COMMENTS 9 :
I have worked in a prawn/shrimp hatchery
in Australia for a mere three years now, witnessing the inexplicable and
making gradual headway on a massive learning curve, working with a fairly
open system.
We now have the opportunity to replace a fairly undersized
filtration and heating system, due to the new input required, and are thus
looking at as many technologies available before we set the new system in
concrete, so to speak.
So far we've looked at a multitude of filtration types,
including
membrane filtration down to 0.2 micron and ozonation, with the latter two
seeming overkill in the conditioning of water, for the very reasons you
stated in your 'open systems' article.
Now comes that ever so pervasive grey area, if not starting
from a clean slate, using expensive technologies, and often changing water
chemistry, how far do we open the system, allowing for minimal water
'bruising' and perhaps even passage to microbiota?
I would be interested in hearing what types of systems are in
use
worldwide, for what reasons. We had a relatively simple open
system of a sand filter, cartridge and bag filters, then UV treatment,
simple though seemingly workable.
Digby Fleming.
E-mail: digbyfleming@hotmail.com
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COMMENTS 10 :
The filtration vs. no filtration in shrimp hatcheries
is an interesting
issue. It can be viewed from several standpoints. Philosophically, I believe
in treating larvae in the best possible way. Most of the larvae from a good
spawn, I believe come equipped to survive, and do well, if the environment
helps. I do not believe that larval batches exhibiting poor survival in the
hatchery will fare better in ponds than good, high survival, batches. The
great majority of hatchery survival problems are related to bacterial
infections. Postlarvae surviving these infections can be compromised and it
stands to reason that they will not do as well in ponds. I believe
just the opposite, that good larval runs lead to good pond results.
As Andy Watkins put it, early larvae are oceanic in nature and at the
hatchery we should do our best to replicate oceanic water quality. This
normally means extensive treatment of coastal water. There are exceptions;
for example, I have heard that Super hatchery in Aruba can operate very well
with a straight ocean intake, due to the great quality of the water there.
For those of us who are not that fortunate, treatment often includes
particle filtration (sand filters, bags, cartridges, diatomaceous earth,
etc.), adsorption processes (activated carbon or protein skimming), and
disinfection (chlorination-dechlorination, ultraviolet light, ozone, etc).
These requirements are site-specific, and for that reason general
recommendations cannot be made.
Postlarvae, especially 10 or 12 days after metamorphosis, do thrive in
"richer" (dirtier) environments, as in nature they normally enter
estuaries. Our group uses an acclimation station to receive early Pl’s,
acclimate them down in salinity if needed, and gradually introduce them to
those kinds of conditions.
A related topic, to get off on a tangent. I've often thought about the algal
densities we use to feed young zoea; they must be higher than those in
nature by several orders of magnitude. Of course in nature the variety of
phyto and zoo-plankton available for the larvae is tremendous, and the
survival of the larvae lower also by orders of magnitude. Any thoughts from
the group?
Lorenzo M Juarez
GMSB Shrimp Hatchery
Summeland Key, Florida. USA
E-mail: ljuarez@seafarmsgroup.com
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COMMENTS 11 :
Good comments. On the issue of feed density,
your note that the
concentrations in the wild are orders of magnitude lower that what
some researchers have claimed to have found to be optimal under
captive conditions, raises some very interesting questions. The same
issue exists for fish larvae relative to live prey items (rotifer densities,
etc).
From some of my playing around, it appears that you get different
results on what is optimal depending upon whether you are pulse
feeding or continuous feeding. With high density larval tanks, they
can clear the feed and get to a very low concentration relatively
fast. Could it be the minimum feed concentration that is the real
variable, not the average concentration?
I like to operate with a continuous input (6 to 10 times/hr) and a
continuous tank discharge (back through the filtration system) which
gives a low (relative to what the literature says is optimal), but
constant density of prey organisms. If you are willing to waste 20%
of your feed to the discharge and use time-variable input (24 hr
cycle) of feed that approximates the consumption, you can hold the
concentration reasonably constant. That is where computer
controlled feeding is handy.
Dallas Weaver
E-mail: deweaver@gte.net
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COMMENTS 12 :
I am doing these tests plus some more for every time
when I am going to stock the ponds, and the results so far have shown that
there is a positive correlation between the results of tests and production.
I have harvested just almost one month ago ponds with average ~55g
body weight in 128 days with FCR of 1.21(P. monodon). I believe PL quality
also playing a very important role here.
Dr. Farshad Shishehchian
Ph.D. Aquatic Ecology- Shrimp Culture Pond Management
Technical Manager (Aquaculture Consultant)
J.W Farm
Malaysia
E-mail: farshadshrimp@hotmail.com