CHECKING FOR PATHOGEN FREE PLS
From: Tommy Chandra tchandra@bhinneka.com
Sent: 5 July 2001
QUESTION:
We are
operating a farm in North Bali, Indonesia where we grow mostly P. monodon.
I would like to know comments/experiences from fellow members on doing a
formalin bath to PLs before introduction into growout ponds. We have read
very often in various publications that this is one of the screening methods
to get healthy PLs. But, I am a bit concerned about the health and stress
levels of the PLs after going through this formalin bath. Would it make them
in higher stress level thus despite that they are stronger, put them into
higher risk of mortality upon introduction into grow out ponds.
A friend also suggested doing a fresh water test, i.e. put a sample of let's
say 100 PLs into 0 salinity water for 10 minutes and then count the survival
rate. Would this method be one practical way in determining the quality of
PL purchased from the hatchery ?
Tommy Chandra
Makara Bumi Satya, PT.
e-mail: tchandra@bhinneka.com
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COMMENTS 1 :
This formalin test is for a sample of PL shrimp,
not for all of them. Yes the idea is to cause them a very high stress to
reveal their weakness or strength. The sampled PL will be discarded at the
end of it.
Eric Pinon
Salinas – Ecuador
e-mail:
epinon@ecua.net.ec
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COMMENTS 2 :
You can use
formalin 20 ppm for 30 minutes before stocking (what I practice and we
have no problems of stress or mortality due to formalin usage). You
can check the health of the PL in many ways, one method I usually do is
check the MGR. If the MGR is 4.5 to
5:1., they are strong and they will survive the salinity shocks in excess of
15 to 20 ppt. If you want to dig a little more on health of fry before
taking them from a hatchery, check the hepatopancreas for signs of MBV
stress. This is one good way of finding out about your hatchery from where
your acquire the fry is able to produce the seeds healthy and in a
stress-free environment.
e-mail: bondadasrinivasarao@yahoo.co.in
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COMMENTS 3:
I have been
hearing different information regarding the formalin test.
I thought we're supposed to do it with all PLs, and only take the survivors
/ strong ones. How many ppm do you usually use ? 100 ppm or 200 ?
Tommy Chandra - North Bali, Indonesia
e-mail:
tchandra@bhinneka.com
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COMMENTS 4 :
I just want to
verify what you have said here:
[1] You treat ALL the PL's that you are to stock into your ponds in this
way?
[2] 20ppm would be 20ml of formalin in 1000 l of seawater?
e-mail: Laurence@amatikulu.co.za
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COMMENTS 5 :
The test as
described to you is for a sample of the PL you buy (or you sell). It is just
another stress test, this one being chemical. As with other stress tests
(salinity, waterflow) you will count survivors or "winners"
against the number of dying / moribond / "losers" according to the
challenge you apply.
You can also go further: not only will you consider the success rate with
the surviving larvae but additionally you can screen the weakest larvae:
take them away and send them for virus check, such as WSSV or others. It is
just a lead of common sense to guess that if you have contaminated shrimp
larvae, they will show in the weaker group... it is not proven but it’s
likely to be.
I am not sure we can apply the same concentrations to all species but as far
as I understand 100 ppm is used for vannamei postlarvae. There are a number
of publications and recommendations about this.
Eric Pinon
e-mail: epinon@ecua.net.ec
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COMMENTS 6:
The local
hatcheries we usually purchase our PLs from are willing to go up to 200 ppm
for P. monodon. But I have my concerns over the conditions of the
survivors/winners. They've been through a high level of stress, would it
affect them when they're introduced into growout ponds?
Tommy Chandra - North Bali, Indonesia
e-mail: tchandra@bhinneka.com
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COMMENTS 7 :
In a paper we
published a few years ago (Samocha, T. M., Guajardo, H., Lawrence, A. L.,
Speed, F. M., Castille, F. L., Page, K. I. and McKee, D. A. 1998. A simple
stress test for Penaeus vannamei postlarvae. Aquaculture 165:233-242) we
have demonstrated the changes in tolerance to formalin and salinity with PL
age. Note that this study was done with PL of one to 7-day-old only.
Tzachi Samocha
e-mail: samocha@falcon.tamucc.edu
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COMMENTS
8 :
I am not sure
but personally I would doubt of the condition of a 200ppm formalin treated
PL for stocking. To prove it’s strength I would use it but not to treat my
stocking PL's.
Eric Pinon