Date: 05 August 1999
From: myrvera@hotmail.com
To: shrimp@onelist.com
QUESTION:
I am trying to find out the best way to wash the nauplii. The CENAIM (here in Ecuador) recently published that iodine and formoline work for certain shrimp varieties, but also said that this method wasn't proven for vannamei yet, any thoughts? If valid, what amounts are proper for the washing process?
I also found a new product in the local market called HALMAQ, which claims to eliminate the WSSV virus as well. Still, I am sceptic about it since I haven't heard anyone who uses HALMAQ successfully.
Alex
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COMMENTS 1:
As you most probably know a variety of products have been used in the past to clean fry, etc. from microorganisms, including Halamid. Talking about shrimp fry, as you most probably know as well, most contamination will happen through contamination from water, tanks, feed (e.g. Artemia) and particularly through faeces from broodstock. Therefore, all different aspects have to be considered and taken into account in order to prevent any possible contamination.
Consequently, I would suggest the following:
- always disinfect the rearing water, tanks and the facility.
- minimize any possible contamination through broodstock faeces by using spawning tanks, where the spawner is kept for the shortest possible time for spawning only and removed immediately after spawning. This can be done, for example, by using e.g. 500-1000 round tanks, where the spawner is placed just prior to spawning and removed immediately afterwards.
- subsequently, wash and disinfect the eggs. Disinfection can e.g. be done by using Halamid: Akzo Chemicals suggests to dip eggs in a 1 gram Halamid per litre solution for 15 minutes; then wash with clean water.
- nauplii: I could not find any information on nauplii. However, for PL's Akzo Chemicals suggests to dip in a halamid solution of 0.1 gram/litre for 15 minutes and wash with clean water afterwards. It would have to be tested on a small batch of nauplii whether this concentration is suitable for nauplii as well. The Artemia 72-hour NOEC (No-Effect-Concentration) is 10 mg/litre.
- wash/disinfect Artemia eggs: Akzo Chemicals has also investigated this and suggests to wash the Artemia eggs for 15 minutes with a Halamid solution of 1 gram/litre, and then wash with clean water.
Infections of early developmental stages (e.g. viral infections) can occur through faecal contamination particularly of the egg shells as we know that from the former MBV problems.
In case you need further information on Halamid or the above information please send an e-mail to:
Dr.Thierry Latscha
Intervet Akzo Nobel
e-mail: Thierry.Latscha@Intervet.akzonobel.nl
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COMMENTS 2:
Chloramine T is the active ingredient of Halamid.
We have tested a US manufactured brand (trade name Halacon) and noted the following:
For Artemia: add 30 ppm at the time that the cysts are being added for
hatching. It eliminates most of the bacteria.
For nauplii: early stage nauplii are very sensitive to the effects of this
and we do not suggest that it be used until N4 or later. They can tolerate a high level (100 ppm for 30 sec). This appears to eliminate all of the bacteria that might be surface associated with the nauplii. Iodine
eliminates about 50%.
For PLs: add to the hatchery tanks to 6 ppm daily to prevent filamentous bacterial problems.
Stephen G. Newman Ph.D.
e-mail: sgnewm@aqua-in-tech.com
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COMMENTS 3:
One of my colleagues working on Nephrops initially had problems with Vibrio. The Vibrio apparently originates from within the Artemia cyst. The way around this is to bathe the Artemia before use in a some sort of chemical to kill off the Vibrio. Hope this is of help.
James Mills
e-mail: millsjor1@hotmail.com
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COMMENTS 4:
Our company INVE AQUACULTURE (+ most other Great Salt Lake harvesting Cies) have had to jump through many hoops in order to prove that Artemia cysts were NOT a vector for shrimp viruses! When the first word of the WSSV hitting Central America became news we voluntarily sent all of our cyst sources to Don Lightner's Lab for analysis. After some initial disconcerting results obtained from false positives on some Primers it was finally confirmed through bioassay and other Primer sets that there were no indications that Artemia cysts were a vector. These tests were carried out at U. of Texas, U. of Arizona, Mexican Gov't Labs + others.
The Vibrio sp. problem can easily be eliminated by putting a product mfg by our company called A1 SELCO at T-0 incubation of cysts...either decapsulated or not. This will suppress the bacterial blooms in the hatching container.
Howard W. Newman
Inve Aquaculture, inc.
e-mail: BShrimp@aol.com
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COMMENTS 5:
Probably worth reminding people that:
1. PCR detects fragments of virus nucleic acid and NOT necessarily viable virus;
2. Many PCR positive results on odd organisms can result from passive
contamination (due to the presence of virus fragments in, for example,
filter feeders, fish stomachs/gills, etc.) in "mechanical carriers". This
is not to say they are all safe, just that positive results by PCR have to be interpreted carefully;
3. The possible existence of different strains of virus which are positive
to some primers but not to others, is still not clear;
4. Two-step (or nested) PCR in particular may have a high rate of false
positives. This is fine for screening out infected individuals (increases
the "safety margin") but not good for diagnosis of virus presence;
5. The more you study it, the more confusing it gets;
6. Psychiatrists make easier money than shrimp farmers.
Recent research suggests that some washing regimes may not be enough to eliminate the virus completely. There are also some suggestions that there is transfer of the virus within the egg but
this requires some further examination of the data as the conclusion depends on the success of a washing protocol.
Dan Fegan
e-mail: fegan@loxinfo.co.th