25 Nov
2008
25 Nov
'08
4:07 p.m.
cher ken
nous avons remaqué en cote d'ivoire que lorsque que nous fesons les pêches de contôle,
les deux jours qui suivent les poissons ne prennent pas correctement les aliments. Le
stress a un effet négatif sur la croissance des poissons. Il nous arrive de trouver de
femelles aussi grosses que les mâles.
Meilleurs salutations
--- En date de : Ven 21.11.08, JF Baroiller <baroiller(a)cirad.fr> a écrit :
De: JF Baroiller <baroiller(a)cirad.fr>
Objet: Re: [Sarnissa-french-aquaculture] [Sarnissa-african-aquaculture] Gender control
for tilapia production Mixed sex graded system
À: "William Leschen" <william.leschen(a)stir.ac.uk>uk>,
sarnissa-french-aquaculture(a)lists.stir.ac.uk
Date: Vendredi 21 Novembre 2008, 17h44
Dear Ken,
It sounds cunning !
My only concern is the effect of successive
stress (the successive sorting for size) on the growth
rate.
A long time ago (when my hair were not white...)
we compare the growth rate of groups of juveniles
(the size at which you should begin the sorting
for size) which were manipulated 5 times (during
a 3 months period) or not manipulated. The growth
rate was strongly inhibited in the manipulated
groups because of the successive stress.
Following your sorting for size, did you also
find some rare females growing very fast ? A few
of them can have growth rate very similar to the males.
Thank you very much for your interesting message.
JF Baroiller
Cher Ken,,
C'est astucieux !
Ma seule inquiètude est que ces tris successifs
constituent des stress successifs avec des effets négatifs
sur la croissance.
Il y a quelques temps (quand je n'avais pas
encore de cheveux blancs...), nous avions comparé
la croissance de groupes de juvéniles (à la
taille où vous devez commencer à voir des
dimorphismes de croissance et où vous commencez
vos tris successifs) qui étaient manipulés
(péchés et aussitôt remis dans leur structure
d'élevage) 5 fois en 3 mois ou au contraire des
groupes que l'on ne péchait jamais. Au bout de 3
mois, les groupes manipulés présentait des poids
moyen beaucoup plus faibles que ceux des lots non
manipulés. La seule différence entre les lots
était la manipulation (même famille, même
densité, même alimentation, ...). Cette moins
bonne croissance était liée au stress des manipulations
successives.
Sinon, quand vous faites vos tris, vous
arrivé-t'il de trouver des femelles dans les
animaux les plus gros ? En effet, on trouve
parfois des femelles qui ont des croissances très proches
de celles des mâles.
Merci pour votre intéressant message,
JF Baroiller
Quand vous faites vos tris, vous arrive-t'il de trouver
At 11:54 21/11/2008, you wrote:
efficiency.
choice?
report
Content-Language: en-US
Content-Type: multipart/alternative;
boundary="_000_8ED3F2CA5B78E142B8193376C57330F8E1958A45B8EXCH2007adsti_"
From: kwbetts [mailto:kwbetts@meabt.com]
Sent: 21 November 2008 06:56
To: William Leschen
Subject: Re: [Sarnissa-stakeholders] Gender control for
tilapia production
Hi,
My situation is a bit unique since I depend on
my fry. Since I have no reliable source of
healthy quality male fry, I raise mixed sex. My
semi-intensive green water recirculated pool
produces about 30 to 40 thousand fry in a year
of which I need up to 11 thousand for grow
out. In the one pool, I have an area of high
density cage nets and about 2/3 of the pool I
intentionally keep stocked with about 100 to 200
breading tilapias. Since my breading season
runs from Oct through Nov and March through
April with winter between them, I catch
virtually all the fry in a baited umbrella net
at a rate up to 800 per day (about 30 minutes
of fishing) taking me through June to catch
almost all of them. Of all that I catch I keep
my grow out needs plus almost 50% extra. Then,
rather than sexing them all, I sort the fish for
size a couple of times in a way that separates
out the slow growers (most of which will be
females) and discard up to 1/3 of all that I
previously kept. So, by the time they reach 100
grams, they are mostly males and have the runts
removed. Of the fastests growing groups of
these, I restock my breading area for the next breading
season.
Manged bi-sex Tilapia. Sound complex? Not
really, its in getting the process
right. Advantages? No need for expensive and
unreliable improted fry. No need for
chemicals. No need for highly reliable and labour
intensive hand sexing.
Ken
On Wed, 19 Nov 2008 11:58:49 +0000, William Leschen
wrote
From
French forum
Dear all,
We all know the importance of sex control for
tilapia production in the majority
of the
numerous farming conditions of this species
group. It is not necessary to remind you all
that numerous techniques have been used up till
now (hybridisation), or is more classically
used for sex control such as manual sexing,
hormonal inversion and use of YY males. Each of
these techniques has been often discussed
showing their advantages and disadvantages. We
all know farmers who use one or another
approach depending on his constraints which are
essentially the cost, the facility for its use and its However,
it is harder to have a relative
estimation of which farmers used which approach.
Would you share this information telling us if:
you use mainly a) manual sexing, b) hormonal
inversion, c) off-springs of YY
males, d)
hybridisation, and mentioning which rearing
conditions you are using (monoculture,
polyculture, extensive or semi-intensive
conditions). Or do you use predators and if it
is the case which species do you use
(Hemichromis, Heterobranchus, Clarias, Lates)?
Finally, what is the main justification of your
Thank you very much,
Helena D'Cotta and JF Baroiller
___________________________________
Dr. Helena D'Cotta
CIRAD-PERSYST
Aquaculture Research Unit, TA B-20/A, Bur.A18
Campus International de
Baillarguet
34398 Montpellier cedex 5, France
Tel : 33 - (0) 467593951; Fax : /3825
<mailto:dcotta@cirad.fr>dcotta@cirad.fr
http://aquatrop.cirad.fr/
PS from Will – See video clip (link below) of
Helena and Jean Francois at work.
>
> Please note clip is in a section of main news >
>
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>
http://jt.france3.fr/regions/popup.php?id=e31a_invite&video_number=0
>
>
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>Checked by AVG - http://www.avg.com
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Dr J.F. Baroiller
CIRAD-Persyst,
UPR20 Aquaculture et gestion des ressources aquatiques
Campus International de Baillarguet
TA B-20/A, Bur.A18
34398 Montpellier cedex 5
France
(: 33.(0)4.67.59.39.51 (ligne directe); 33.(0)4.67.59.39.05
(sec)
Fax : 33.(0)4.67.59.38.25
* baroiller(a)cirad.fr
http://aquatrop.cirad.fr/
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