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@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@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 > > _______________________________________________ >

No virus found in this incoming message. Checked by AVG - http://www.avg.com Version: 8.0.175 / Virus Database: 270.9.8/1800 - Release Date: 11/19/2008 6:55 PM _______________________________________________ Sarnissa-african-aquaculture mailing list Sarnissa-african-aquaculture@lists.stir.ac.uk http://lists.stir.ac.uk/cgi-bin/mailman/listinfo/sarnissa-african-aquacultur...

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

------------------------------------------------------------------------

_______________________________________________ Sarnissa-african-aquaculture mailing list Sarnissa-african-aquaculture@lists.stir.ac.uk http://lists.stir.ac.uk/cgi-bin/mailman/listinfo/sarnissa-african-aquacultur...