SHRIMP NAUPLII AND PL QUALITY
QUESTION:
Farms do a stress test with hatchery PL's. Do you do a stress test with
your maturation nauplii ? I played around with this in Mexico in the 80's.
I suppose your problem may be then that you will need perhaps to build
more larvae grow-out phases to supply the larvae necessary for the
company. So perhaps it is a question of size but perhaps internal relative
size of your larval grow out to your maturation to your final needs (the
supply chain.....).
Patrick Wood
E-mail: patjwood@hotmail.com
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COMMENTS 1 :
Stress tests for nauplii quality assessment were mentioned in a previous
posting. I am curious to learn more about them. Nauplii quality can vary a
lot between seasons, between spawner batches, between spawners in the same
tank, and between spawns from the same female. Broodstock diet is even a
more important factor. We found correlations between nauplii quality and
larval quality (zoea and mysis) and other reports correlated it with PL
quality. Therefore, nauplii quality assessment should be a crucial step in
the hatchery
process.
Nevertheless, all the nauplii that hatch in one day are generally
pooled and the only selection that is carried out routinely is
phototropism. Other evaluation criteria like % deformities and colour have
also been proposed, but are not applied frequently. More complex
techniques like biochemical analyses are only used for research purposes,
though Palacios et al. (CIBNOR, Mexico) developed simple techniques with
chemical kits. Toxicity tests are probably not suitable since nauplii are
robust and depend on yolk reserves (correct me if I am wrong on this one).
Roeland Wouters
E-mail: rwouters@cenaim.espol.edu.ec
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COMMENTS 2 :
Would you care to elaborate a bit on how you assessed nauplii quality
and subsequent mysis quality? My impression of "accepted" PL
quality
determinants is that they often bear little relation to ultimate
performance of PL batches in nursery or grow-out. For example, using
salinity stress tests many years ago we found that a substantial
percentage (> 25%) of batches that would have been rejected for
stocking based on stress tests in grow-out performed as well as, or better
than, batches that would have been accepted based on the same parameters.
Similarly, a substantial number of batches that were accepted performed
poorly on grow-out. Obviously, comparing the survival of PLs after a
salinity and/or temp shock to pond harvest results is a bit of a long shot
but there are a lot of farmers doing
just that.
The stress test concept (salinity & temperature shocks) along
with other measures of "quality" such as swimming activity,
lipid levels etc as determinants of PL quality have often been touted yet
I don't think I have ever seen anything quantitative that supports the
concept, at least for P. vannamei.
Will increased domestication improve the use of quantitative tests as
the genetic variability from batch to batch diminishes?
David Griffith
E-mail: dgriffith@seafarmsgroup.com
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COMMENTS 3 :
We are doing PL quality test for almost past 2 years, and it is helping us very much. Salinity test is just one of them, I check for hepatopancras, G-M ratio, necrosis, fouling and some others. I strongly believe that those larvae, that are able to pass the tests, significantly perform better in the growout ponds.
Farshad Shishehchian
Ph.D. Aquatic Ecology- Shrimp Culture Pond Management
Technical Manager
J.W Farm
Malaysia
E-mail : farshadshrimp@hotmail.com
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COMMENTS 4 :
Nauplii quality, or should I say "offspring quality" was
estimated by
parameters like % hatch, fototropism, naupliar deformities, naupliar
length, FA composition. We find these to be related to % survival up to
the zoea and mysis stages, and to zoea length and mysis length. Palacios
and co-workers report positive correlations between PL 15 osmotic stress
survival and naupliar length, naupliar biochemical composition, naupliar
condition index (NCI) for L. vannamei.
Whether PL quality is related to final grow-out... . Well, it should
be, but I understand that there are no research data to back up this
theory. It would take a great effort to test this in a statistically
sound manner. Maybe your selection criteria were too strict. Maybe your
stress test lacked fine-tuning and rejected PLs that were still good
enough. In my opinion, the least PL quality assessment tests will do is to
provide useful information on PL quality at the very moment they are
carried out. This information could be used to predict PL performance
during transport, handling and stocking into the ponds. Extrapolation to
grow-out output is probably difficult because a number of factors
interfere, and because the initial poor-quality PL may catch up with the
initial good-quality PL during grow-out in terms of growth and resistance
(unless they died). I guess that if PL quality differences were to be
really extreme, you would indeed see its effect on the long term.
Though genetic variability is just one source of error, it is indeed
probable that quality tests will become more predictive under more
controlled rearing conditions. Improving the quality tests themselves is
yet another challenge. But is the shrimp industry really interested?
Patrick, what kind of nauplii stress tests were you performing in
Mexico?
Roeland Wouters
E-mail: rwouters@cenaim.espol.edu.ec
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COMMENTS 5:
The usual light, temperature, with/without EDTA stuff, also leaving them in the hatching tank till Z1/2 with a home made feed mix, no algae, and then roughly netting them out. I suppose this last one isn't much of a test more like a physical selection process...results 25% survival at pl8 (estimated because no counting was done 'till end), strong larvae and the USNMFS kona SPF strain....
Patrick Wood
E-mail: patjwood@hotmail.com
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COMMENTS 6:
As for the relation PL-quality and performance in grow-out, we did two
studies here in Vietnam relating PL-quality to 1) performance during
transport 2) performance in grow-out. The first study gave very
significant results (using both a multiple regression and individual
correlations) for quality criteria (swimming behaviour; uropods; antenna;
MGR; zoothamnium infestation = the Watchana-Sunthorn method) but indeed
relations between performance during transport (we used a standardized
transport simulation of 24 hours) and stress-test (using deionzed water
and different concentrations of formol) was poor (I should check but I
seem to remember only formol 200ppm after 24hours gave a significant
correlation). The sample was definitely random (= we had wide range of
qualities)but small (only 15); so some caution is recommended.
As for the second set of experiments, they are still going on. We are
following 15 ponds + did a stocking experiment with one pond bad, one pond
good and one pond mixed (shrimp are tagged so we can separate the groups).
A first impression is (but this should be confirmed!!) that the main
effect of PL-quality is in initial survival (and of course survival during
transport). After this, other factors (i.e. pond management, feeding water
quality etc.) seem to become more important. As it are most likely the
weak PL which are first eliminated in the "bad quality badges"
and as a result stocking density becomes lower in these ponds (which
considering the management + stocking densities as used in Vietnam can be
considered as an advantage) this will further reduce the difference in
growth-rate between the two groups.
So in summary, I was also very sceptical where these tests were
concerned (which is why we tested them) but it looks like they do have
their use.
Peter Baert
E-mail: roblescarmen@hotmail.com
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