4 Dec
2008
4 Dec
'08
1:27 p.m.
Ces propos de Owori correspondent bien aux résultats de Cyrille, et
milite en faveur d'une caractérisation approfondie ('"normalisation") de
l'association clarias - tilapia mixte (mâles et femelles)...
Olivier
Cher Macharia,
Notre expérience sur l'utilisation du Clarias en aquaculture en Ouganda
montre que :
i quand on récolte un petit nombre de très gros /Clarias,/ cela tend à
signifier un niveau élevé d'alimentation non approprié qui favorise le
cannibalisme des plus gros sur les plus petits. Mais quand
l'alimentation est adéquate, la variation de taille est réduite. des
résultats similaires sont trouvés par Hecht et al (2000).
ii La taille des proies est corrélée par la taille des prédateurs. De
très gros /Clarias/ peuvent consommer de gros tilapias qui déjà bon pour
la consommation humaine.
iii Cependant, quant la nourriture est adéquate, le clarias ne consomme
pas les proies vivantes (coût énergétique élevé de la poursuite de la
proie vivante). C'est pourquoi, le niveau d'alimentation doit être
contrôlée pour permettre un contrôle effectif de la population de
tilapia par les Clarias.
Owori
----Original Message-----
From: sammy Macharia [mailto:sammacharia@yahoo.co.uk]
Sent: 20 November 2008 09:18
To: William Leschen
Subject: Re: Gender control for tilapia production
To French Team
In Kenya, hand sexing is commonly used but with only about 60% success.
Clarias is used as a predator in a biological control setup, this is not
very success because one may end up with a few big caftfish that are not
effective in controlling the tilapia proliferation.
Macharia
owori wadunde a écrit :
Dear Mr. Macharia,
Our experience with the use of Clarias gariepinus in aquaculture in
Uganda include the following:
i. When one harvests only a small number of very large Clarias, it
tends to mean a high level of inadequate feeding that forces the
larger individuals to cannibalise on the smaller ones But when feeding
is adequate, size variation is minimised. Similar findings were also
made by Hecht, et al. (2000).
ii. Prey size is correlated with predator size. Therefore, very large
size catfish may feed on large tilapia that is good enough for human
consumption.
ii. On the other hand, when feeding is adequate, the catfish is not
effective at feeding on live prey (high energy cost of chasing live
prey). Therefore, feeding must be controlled to some level to allow
the catfish effectively control the tilapia population.
Otherwise we have had a number of cases of successful control of
tilapia populations using the catfish
God bless,
Owori
*/William Leschen <william.leschen(a)stir.ac.uk>/* wrote:
-----Original Message-----
From: sammy Macharia [mailto:sammacharia@yahoo.co.uk]
Sent: 20 November 2008 09:18
To: William Leschen
Subject: Re: Gender control for tilapia production
To French Team
In Kenya, hand sexing is commonly used but with only about 60%
success. Clarias is used as a predator in a biological control
setup, this is not very success because one may end up with a few
big caftfish that are not effective in controlling the tilapia
proliferation.
Macharia
--- On Wed, 19/11/08, William Leschen wrote:
From: William Leschen
Subject: [Sarnissa-stakeholders] Gender control for tilapia
production
To: "sarnissa-stakeholders Mailing
List"
Date: Wednesday, 19 November, 2008, 11:58 AM
Translated 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(a)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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Senior Research Officer
The National Agricultural Research Organisation
Aquaculture Research and Development Centre
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UGANDA
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