1 OKTOBER 1999
CLEAN SHRIMP SEED
COMMENTS 1:
Sent: August 12, 1999
From: Jim Wyban <wyban@gte.net>
To: <shrimp@onelist.com>
It is now clear that wild shrimp present a serious threat to farming activities. While WSSV prevalence in wild animals (PL and broodstock) may fluctuate over time (well documented in Taiwan), WSSV presence in the wild will continue.
The most sensible management responses to the WSSV problem are to stock clean seed and management by exclusion. Simply said, difficult to apply. For clean seed, closed systems with pond reared broodstock with a documented WSSV-free history is the best method to produce clean seed. Nauplii disinfection followed by PCR screening of PL is the alternative. This method is better than no screening but often produces false negatives where seed are scored clean but actually carry the virus. Use of these seed can put an entire farm crop at risk. The only sure way of producing clean seed is starting with certified virus free broodstock.
Many companies are now starting breeding programs. While the general concepts of breeding shrimp are straight forward, there are many subtleties that can affect the outcome. My company has many years of experience in breeding shrimp and producing healthy nauplii and PL. We are pleased to announce that we have launched a consulting division to help the industry in the areas of shrimp breeding, broodstock culture and production of clean PL. Further information is available on our webpage http://www.hihealthshrimp.com ).
Jim Wyban PhD
High Health Aquaculture, Inc.
ph/fax: 808-982-9163
e-mail: wyban@gte.net
http://www.hihealthshrimp.com
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COMMENTS 2:
Although I agree with your comments I would like to add that false negative when appropriate PCR procedures are followed are not produced "often".
Producing nauplii and PL from "clean" broodstock is no guarantee either since the virus can come in with water born carriers at any stage of the grow out. Also and paradoxically, the "clean" broodstock must be certified using the same PCR technology that could give false negatives.
I still think it is a good idea to have WSV-free broodstock, but I think it is even more important to have a strict protocol to disinfect nauplii and hatchery water in a very effective manner.
Boli, farallon1@pananet.com
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COMMENTS 3:
From my experience (at least in Ecuador), the ones that say that their
maturation labs have ONLY virus free broostock, are either fooling
themselves or trying to fool others. The reason is that it is economically and logistically impossible to check every single shrimp. Even if these labs send samples to be analyzed and these return negative, this doesn't allow to state that they don't have the virus (a "sample" is just a representation of the population, a percentage, not the entire amount).
Here in Ecuador the situation is even worse, because ALL the shrimp of EVERY maturation facility WORKS WITH WILD SHRIMP (I find hard to believe that someone here is so advanced to work ONLY with non-wild shrimp; it is also economically unfeasible given the actual prices of the nauplii). The virus started manifesting in Esmeraldas, a province near Colombia, and since then it has propagated and cases have been reported practically all over the
country. Still, some labs state that they haven't bought broodstock from the regions affected, and that they don't have the virus therefore.
Unfortunately, not everybody has the curiosity to find out more info about WSSV, and actually believe this crap.
I believe that the one and only way to prevent the virus is by disinfecting the nauplii and eggs appropriately. I also believe that every maturation lab in Ecuador has the virus somehow, and that it is unethical, as I have found myself, labs that state that they are totally virus free. Unfortunately, I have seen people who actually show PCR analysis to verify what they say. So, by now the only way that I see to have virus free larva is to ask for PCRs of the nauplii being bought, not the broodstock. This still doesn't protect you 100% as people on the list have confirmed in previous messages, but what else can you do?
Alex, myrvera@hotmail.com
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COMMENTS 4:
I apologize if my use of "often" sounded too strong but based on the results I have been seeing, it seemed appropriate. Error frequency (false negatives and false positives) in PCR can range from rare to too often. Quality Control of PCR analyses is a science in itself and is largely influenced by technician experience. Since this technology is very new to the shrimp industry, many mistakes will be made. Because these results are going to have a huge impact on the future of the industry, it is important that concerted efforts be made to standardize and improve PCR QC.
Concerning your point that certified broodstock producers and PL producers are both constrained by the technical limitations of PCR, there is an important difference. For certified broodstock, a stock history is developed that represents months or years of repeated sampling. Even though one sample may be inaccurate, with repeated sampling over time, precision and confidence in the certification is very high. In contrast, by testing PL only, the producer (and buyer) is dependent on the accuracy of a single sample (in time). Probably the best solution to produce clean seed will be a combination of these techniques.
Jim Wyban PhD
High Health Aquaculture, Inc.
visit our new webpage: http://www.hihealthshrimp.com
ph/fax: 808-982-9163
e-mail: wyban@gte.net