25 Nov
2008
25 Nov
'08
5:25 p.m.
Dear Jean Francois - translated reply from Ken.
Amicalement
Will
Salut JF,
Merci pour vos commentaires. Je ne suis pas vraiment la capacité de test pour des périodes
successives de stress car je n'ai qu'une piscine et ne peut donc pas exécuter un
groupe de contrôle. Toutefois, je ne suis en déduire les taux de croissance qu'il est
petit. Par rapport à la norme de swimup-GM-450 en neuf mois-je obtenir environ 60% le taux
de croissance. Mixte de poissons, où les femmes semblent croître à environ 55% de taux
d'hommes, une distribution de 2:1 M: F, indique environ 85% de croissance en moyenne.
Cela impliquerait que je suis la réalisation sur seulement 70% de mon taux de croissance
potentiel. Toutefois, la croissance des exploitations agricoles (stock d'environ 3
poissons par mètre carré) dans ma région, qui sont importés à l'aide de la RFY, stock
30 jours tous les hommes en avril et ont un poids moyen de seulement 350 grammes par
Novembre (environ 78 % De la norme figure). Ainsi, par rapport à ce chiffre, je suis
atteindre environ 90% de la ferme, d'autres taux de croissance.
Après quelques années de tri, j'ai trouvé que 3 sortes (environ 35 g, 70 g GM 110),
donne-moi un ensemble ordonné de la poissons. Je ne sorte plus de deux fois au cours de
croître à. Comptage de la capture de l'original, qui fait un total de six sortes au
cours du cycle de vie. Depuis poissons de taille similaire, semblent faire mieux ensemble,
je suppose que certains qui compense le stress. Tri à la nuit semble aussi produire
beaucoup moins de stress que le tri dans la journée.
Depuis ma piscine est continue la production et les ventes, j'ai vraiment besoin de
leur triés régulièrement pour les ventes de toute façon.
Aussi, j'aime bien la stabilité d'être en mesure de produire mon propre alevins.
J'ai trouvé que les femmes semblent tenir à leur groupe d'âge de sexe masculin.
Tout d'autres suggestions sur la façon d'augmenter la croissance et de réduire le
stress etc alors que la gestion d'un bi-sexe tilapia ferme sont les bienvenus.
Ken
From: sarnissa-african-aquaculture-bounces(a)lists.stir.ac.uk
[mailto:sarnissa-african-aquaculture-bounces@lists.stir.ac.uk] On Behalf Of kwbetts
Sent: 22 November 2008 09:14
To: sarnissa-african-aquaculture Mailing List
Subject: Re: [Sarnissa-african-aquaculture] FW: Gender control for tilapia production
Mixed sex graded system
Hi JF,
Thanks for your comments. I don't really have the ability to test for successive
stress since I have only one pool and so cannot run a control group. However, I do infer
from growth rates that it is small. Compared to the standard swimup-to-450 gm in nine
months I get about 60% growth rate. Mixed fish, where females seem to grow at about 55%
of rate of males, a 2:1 distribution of M:F, would indicate about 85% growth on average.
That would imply that I am acheiving only about 70% of my potential growth rate. However,
the grow out farms (stocked at about 3 fish per sq meter) in my area, that are using the
imported fry, stock 30 day old all males in April and have an average weight of only about
350 grams by November (about 78% of the standard figure). So compared to that figure, I am
acheiving roughly 90% of the other farm's growth rate.
After a couple years of sorting, I have found that 3 sorts (about 35 gm, 70 gm 110 gm),
gives me a well ordered set of fish. I do sort them two more times during grow out.
Counting the original catching, that makes a total of six sorts during the life cycle.
Since fish of similar size seem to do better together, I guess that that offsets some of
the stress. Sorting at night also seems to produce a lot less stress than sorting in the
day.
Since my pool is continuous production and sales, I really do need them sorted regularily
for sales anyway.
Also, I really like the stability of being able to produce my own fry.
I have found females that appeared to keep up with thier male age group.
Any additional suggestions of how to increase growth and reduce stress etc. while managing
a bi-sex tilapia farm are most welcome.
Ken
On Fri, 21 Nov 2008 16:45:03 +0000, William Leschen wrote
From: JF Baroiller [mailto:baroiller@cirad.fr]
Sent: 21 November 2008 16:45
To: William Leschen; sarnissa-french-aquaculture Mailing List
Subject: Re: [Sarnissa-african-aquaculture] Gender control for tilapia production Mixed
sex graded system
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:
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 efficiency.
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 choice?
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
dcotta@cirad.fr<mailto: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 report
http://minilien.com/?aPNxm6nYpr
http://jt.france3.fr/regions/popup.php?id=e31a_invite&video_number=0
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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
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