New subject: [Sarnissa-french-aquaculture] [Sarnissa-african-aquaculture] Gender control for tilapia production Mixed sex graded system

21 Nov 2008

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
 <mailto:dcotta@cirad.fr>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://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: 270.9.8/1801 
- 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/
-------------- section suivante --------------
Une pièce jointe HTML a été nettoyée...
URL:
http://lists.stir.ac.uk/pipermail/sarnissa-french-aquaculture/attachments/2…

Re: [Sarnissa-french-aquaculture] [Sarnissa-african-aquaculture] Gender control for tilapia production Mixed sex graded system