Ce n'est normalement pas un problème lorsqu'on utilise des hapas, à moins que les opérateurs ne parviennent pas à enlever les alevins qui ont été crachés par les femelles quand ils étaient en train d'encombrer les couveuses dans le hapa. Je peux comprendre que toutes les fermes n'ont pas des travailleurs aussi prudents qui se soucient ou qui sont correctement formés et c'est donc tout à fait possible.
Karen L. Veverica
Directeur, E.W. Shell Fisheries Research Centre
École des pêches, de l'aquaculture et des sciences aquatiques
Université d'Auburn, AL USA
From: Karen L. Veverica [mailto:veverkl@gmail.com]
Sent: 12 March 2018 16:44
To: Gerd Teunissen <agerdteunissen(a)gmail.com>; sarnissa-french-aquaculture Mailing List <sarnissa-french-aquaculture(a)lists.stir.ac.uk>; William Leschen <william.leschen(a)stir.ac.uk>; sarnissa-african-aquaculture Mailing List Return Address <sarnissa-african-aquaculture-bounces(a)lists.stir.ac.uk>
Subject: Re: [Sarnissa] reminder for tilapia hatchery operators
It normally isn't a problem when using hapas unless the operators are failing to remove any fry that were spit by females when they were crowding the brooders in the hapa. I can figure that not all farms have equally careful workers who care or who are properly trained and so it is quite possible.
Karen L. Veverica
Director, E.W. Shell Fisheries Research Center
School of Fisheries, Aquaculture and Aquatic Sciences
Auburn University, AL USA
office: 1-334-844-4667
cell: +1 334-332-1560
On 3/8/2018 8:43 PM, Gerd Teunissen wrote:
Does this also happen when you use hapas?
De: Sarnissa-french-aquaculture [mailto:sarnissa-french-aquaculture-bounces@lists.stir.ac.uk] Em nome de Randall Brummett
Enviada: quinta-feira, 8 de março de 2018 16:18
Para: Karen L. Veverica; sarnissa-french-aquaculture Mailing List; William Leschen (william.leschen(a)stir.ac.uk<mailto:william.leschen@stir.ac.uk>); sarnissa-african-aquaculture-bounces(a)lists.stir.ac.uk<mailto:sarnissa-african-aquaculture-bounces@lists.stir.ac.uk>
Assunto: Re: [Sarnissa] reminder for tilapia hatchery operators
We had this problem all the time in Malawi with T. rendalli. After two weeks, fry production started down because we couldn't catch all the juveniles that were eating them. Had to take the pond apart and start over.
From: Sarnissa-african-aquaculture [mailto:sarnissa-african-aquaculture-bounces@lists.stir.ac.uk] On Behalf Of Karen L. Veverica via Sarnissa-african-aquaculture
Sent: Thursday, March 08, 2018 9:32 AM
To: sarnissa-african-aquaculture(a)lists.stir.ac.uk<mailto:sarnissa-african-aquaculture@lists.stir.ac.uk>
Subject: Fwd: reminder for tilapia hatchery operators
here it is again, Will
-------- Forwarded Message --------
Subject:
reminder for tilapia hatchery operators
Date:
Sat, 3 Mar 2018 10:48:55 -0600
From:
Karen L. Veverica <veverkl(a)gmail.com><mailto:veverkl@gmail.com>
To:
sarnissa-african-aquaculture(a)lists.stir.ac.uk<mailto:sarnissa-african-aquaculture@lists.stir.ac.uk>
I was chatting with Evans Danso in Ghana via WhatsApp recently about a problem he was having with reduced output in his tilapia fry production. Reasons can be several but the first one I mentioned was leftover fry/fingerlings that can cannibalize the new fry. Upon further discussion, he told me they harvest fry twice a day from the ponds and the photo he sent showed the long, narrow ponds. He decided to see if cannibalism was the case and drained the pond and did find a few fingerlings in there. He then dissected some and sent me a photo. One small fingerling had 28 fry in its stomach- see attachment. He sent several more photos, all of very small tilapia having very full stomachs and intestines of tilapia fry.
Normally, hapa spawning can prevent this from being a problem but only if the operators are very careful not to leave any fry or fingerlings in the hapa. Draining spawning ponds after every cycle is also a means of preventing cannibalism and thus increasing fry production but it requires the operator to dry the pond between sessions and make sure no fry are left in nests.
We also discussed how the females can be synchronized, which is often a practice that is beneficial but that means fry production will be high for a few days and then drop off until the females all spawn again. So somebody who collects daily would normally notice a drop in fry collections and then they would pick up again.
Other reasons for a drop in fry production are:
* cool temperatures- this will increase time for spawning and egg hatching; and even stop spawning
* chronic low oxygen levels (those of you with hapas should be careful here, especially if you are letting the sides of the hapa foul)
* low nutritional condition of the broodstock- especially the females. This is remedied by giving the females a resting time in a pond or hapa with no males present.
* build up of predator insects and frogs in pond or hapa
Do any of the readers have other observations to share? A big thanks to Mr. Danso for providing the photo.
Karen L. Veverica
Director, E.W. Shell Fisheries Research Center
School of Fisheries, Aquaculture and Aquatic Sciences
Auburn University, AL USA
office: 1-334-844-4667
cell: +1 334-332-1560
