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 No virus found in this incoming message. Checked by AVG - http://www.avg.com<http://www.avg.com/> Version: 8.0.175 / Virus Database: 270.9.8/1801 - Release Date: 11/20/2008 9:11 AM _______________________________________________ Sarnissa-african-aquaculture mailing list Sarnissa-african-aquaculture(a)lists.stir.ac.uk http://lists.stir.ac.uk/cgi-bin/mailman/listinfo/sarnissa-african-aquacultu… 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/ <http://aquatrop.cirad.fr/> No virus found in this incoming message. Checked by AVG - http://www.avg.com Version: 8.0.175 / Virus Database: 270.9.8/1801 - Release Date: 11/20/2008 9:11 AM