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

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 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. estimation of which farmers used which approach. 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? Campus International de Baillarguet Helena and Jean Francois at work. 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…