New subject: [Sarnissa-french-aquaculture] joyeux Noël

4 Dec 2008

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 &lt;william.leschen(a)stir.ac.uk&gt;/* 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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 A.Owori-Wadunde
 Senior Research Officer
 The National Agricultural Research Organisation
 Aquaculture Research and Development Centre
 P.O.Box 530
 KAMPALA
 UGANDA

 Celophone: 256 772 502 966

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Re: [Sarnissa-french-aquaculture] [Sarnissa-african-aquaculture] Gender control for tilapia production Kenya