ROTATING VANNAMEI –
MONODON culture
From: Freddrick Poh fredpoh@starhub.net.sg
To: shrimp@yahoogroups.com
Sent: 24 March 2003
QUESTION:
Right now, there is a belief that, when a country
grow out pond used to grow monodon then switch to vannamei, and when they
have disease problems with the vannamei, and the farmers want to switch back
to monodon, it is impossible as the pond is contaminated or whatever the
reason, the pond will no longer be able to accommodate back monodon for
farming. At the end of the day, both species can no longer be cultured.
e-mail: fredpoh@starhub.net.sg
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cOMMENTS 1:
Presently, Malaysia is successful now with the
vannamei, but it seems like always the initial success only. It has not
happened yet in Malaysia.
Basically, it very hard for the SPF PL to stay pricing competitive over non
SPF PL, and most farmers are not well informed or have no experience in
vannamei, and when the virus starts to kick in, it seems too late to do
anything to rectify the problems. Even, introducing SPF broodstock, it not
easy for the broodstock to stay SPF, when your surrounding is full of
pathogens. As hatcheries in South East Asia and even farmers mostly belong
to small scale and not the multi national company style, they will not have
huge funds to invest in the equipments, well designed hatchery, etc, etc.
Freddrick
e-mail: fredpoh@starhub.net.sg
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Comments 2:
I understand the problems you are facing keeping SPF
stocks clean in
that environment etc. unscrupulous hatcheries, and how vannamei will do well
the first crop etc.... But that doesn't explain the phenomenon you mentioned
of monodon doing poorly when farmers switch back from attempting to culture
vannamei. Are there actual cases where farmers have switched back to
monodon after having failed in vannamei and done worse than before the
change to vannamei? Where, as you said, it seems that vannamei
"ruined" the pond for monodon? I find this very interesting
if it's true.
I don't really think that rotating shrimp in ponds would be beneficial
in the way that rotating crops in soil is. Instead of switching from say,
corn to soy beans, or letting a field go fallow, changing shrimp species
would be more like switching from white corn to yellow corn. And, this is of
course referring to all of the farmers who still use soil for pond bottoms.
Hank
e-mail: Bauman.BAL@starband.net
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comments 3:
Without more technical information on exactly what
you mean by "the pond is contaminated", it is difficult to render
an opinion; but, I suspect that the move by the authorities in Malaysia to
restrict the farming of vannamei in that country (if it is indeed true) is
due to a combination of:
1. Inaccurate technical information.
2. Misinformed government authorities.
3. Persons or entities with a self-serving interest in
restricting access
by Malaysian farmers to alternative species for culture.
The idea that the presence of one species of shrimp in a pond could
"contaminate" the pond, rendering it uninhabitable for another
similar
species sounds unreasonable, UNLESS the first species introduced was
carrying a pathogen that could jeopardize the health of the shrimp cultured
in the subsequent crop. For that reason, only certified, disease-free, SPF
or "high health" vannamei should be stocked and farmed in
Malaysian shrimp farms, thus minimizing the risk that any pathogens
introduced with the vannamei could jeopardize future production cycles from
those same ponds. Of course, if you mismanage a shrimp pond, no matter what
species of shrimp it contains, for example overfeeding, exceeding the pond's
carrying capacity, or not properly
conditioning the pond bottom after harvest, the pond's conditions might be
hostile for any species of shrimp in the subsequent crop.
There is nothing unique about the behavior of vannamei in a pond that would
cause the pond to become uninhabitable for subsequent reintroduction of
monodon at a later date. In fact, vannamei's ability to grow and perform
well on low-protein diets, and to attain high yields with relatively low
FCR's signify that the lower nitrogen and organic matter inputs into the
pond would actually result in better pond bottom conditions when compared to
other shrimp species. The reality is that species rotation (like crop
rotation) might be an interesting production strategy for some farmers.
Henry C. Clifford III
Technical Director
Shrimp Improvement Systems
e-mail:
hcclifford@aol.com
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cOMMENTS 4:
Contaminated in the sense that, most probably, is
introducing others virus for example, Taura. Basically, I understand the
virus is going to affect any species you are going to culture. My posting is
to find out more info on, as you mentioned, if there is any behavior of
vannamei in a pond that would cause the pond to become uninhabitable for
subsequent reintroduction of monodon at a later date. I think I got that
clear. But right now the problem is how many hatcheries out there are using
SPF or SPR vannamei; I could say very few. China has huge success for the
initial SPF broodstock, but after that they fail with their
"local" and SPF broodstocks, and face more problems than before
when they switch back to monodon at a later date. They seem to have problems
with Taura, IHHN. Actually, before vannamei is being introduced, monodon is
more or less adapted to WSSV.
This fact has already happened in Thailand and China, if I’m not wrong.
Freddrick
e-mail: fredpoh@starhub.net.sg
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coments 5:
I know very little about Malaysia, but it's possible
the government there may have one good reason to worry about introduction /
massive culture of additional species. It is the case in Latin America at
any rate that you can pretty much count on some farmer taking shortcuts on
the seedstock issue and thus import diseases additional to the locally
endemic ones. No amount of detailed regulations seems capable of preventing
this in our context and possibly in theirs as well. Thus only an outright
ban is left as an option.
Additionally - and I'm shaky on this one - is it not the case that both
species differ in their degree of susceptibility to specific viral
diseases, and therefore large-scale culture of, say, vannamei could greatly
amplify the water-system load
of some preexisting virus (which monodon can tolerate at low loads) and thus
cause the medium-term "contaminating" effect that Freddrik
mentions?
As I say my epidemiology knowledge is limited indeed, but the previous
paragraph is my interpretation of comments I've heard from more than one
authority on shrimp disease. True enough, it disagrees with the favourable
experiences with agricultural crop rotation you mention. But in the latter
case I think the experience is with very different species, not with close
cousins as vannamei & monodon are.
Your comments on pond-mismanagement are right on.
Julio
e-mail: julioe@speed.net.ec
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COMMENTS 6:
I did not imply you were suggesting that Malaysia (or
Asia) should convert to vannamei. Where "good" species of
shrimp for aquaculture are endemic, I truly believe that preference should
be given to culturing that/those local species rather than importing foreign
species.
Though I'm sure you probably can cite numerous cases where SPF shrimp have
been successfully cultured when surrounded by disease, I think you will
probably find just as many or more references to situations where SPF
animals have failed miserably in neighbourhoods hot with shrimp diseases.
Our mutual experience with Super Shrimp in Mexico and recent history in
Belize are the latest testament to this.
In order to avoid the introduction of new diseases, it certainly makes
sense to attempt to regulate and enforce the restriction that all imported
animals be SPF. The story of the introduction of IHHN with monodon in
South America (back in the '70's) is a perfect example of why.
However, once the animals are in country (or anywhere nearby), it will be
extremely difficult to control their origin and movements, especially when
smuggling of broodstock is such a rampant practice (as it is in many places
in Asia).
My point is still the same. SPF is a great idea if you can truly
manage
and control your system to avoid contamination, a task that is often beyond
the capabilities and/or means of the average, non-corporate, shrimp farmer.
If you can control your environment, then whenever possible, I'm in favor of
emphasizing the development of SPF lines of aquaculture tested and proven
local species/strains of shrimp.
Josh
e-mail: joshwilkensfeld@mindspring.com
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Comments 7:
My comments about species rotation were merely
addressing two issues:
1. As Julio pointed out, some species of shrimp do differ in
their degree of susceptibility to CERTAIN pathogens, and so you might be
able to take advantage of that fact by alternating species on a crop
rotational basis; or trying to coincide with seasonal differences in disease
incidence. For example, if a particular disease is seasonal in your area,
stock the shrimp species that is most resistant to it during the
"peak" season.
2. Some shrimp species differ in their behavior in the ponds,
for example their foraging behavior, diurnal activity patterns, or other
behaviors; and so the idea would be to rotate species in order to create
better, more sustainable conditions in the pond. As an example; vannamei and
stylirostris have very different feeding and foraging behaviors, and I had
some clients who stocked both species in their ponds (in monoculture) and
later would comment how the bottoms of the vannamei ponds seemed to be
cleaner, presumably because of their greater tendency to actively forage in
the pond sediments, and because stylirostris tend to be more wasteful in
feeding (resulting in higher FCR's). But I confess that this idea is more
speculative than empirical because I do not know if these differences in
feeding behavior
would translate into meaningful differences in pond bottom quality, and of
course, as Hank alluded to, this might only have a benefit in earthen ponds.
I would rather let an experienced epidemiologist weigh in on the suggestion
that vannamei could "amplify the water system load of some preexisting
virus" that does not effect monodon until it reaches a critical mass,
but I am skeptical of this theory because it infers that no other suitable
hosts or vectors for that virus coexist in the environs of the monodon, and
that the introduction of a single crustacean species is the necessary
trigger for the "amplification". There are more than 60 known (and
probably 100's more) hosts/carriers/vectors for WSSV, and I dare say the WSS
virus does not depend exclusively on any one of those many vectors to be
present in the environment in order to establish its transmission pathway.
I really do not wish to get dragged into the thread about banning or not
imports into a particular country. That is a decision that local authorities
have to make. Unfortunately, it is usually the case that the decision to
restrict imports is taken long after nasty pathogens like WSSV or TSV are
already in their countries, due to illegal or unauthorized importations from
countries and suppliers who are already infected with the pathogen. The only
point that I was trying to make is that there are suppliers who are
disease-free, and can prove it. It is up to the appropriate authorities to
decide if they want to make an effort to determine who is clean and who is
not.
Henry
e-mail: hcclifford@aol.com