One Response to “Science Project Tilapia..! (1st Qtr. 2011)”

  1. JRMarchesini says:

    Dear Jackalope:

    I read your article. It was interesting. But you should be aware of a few inconsistencies. So let me make clear some of them.

    1) A Hybrid is a mixture of different subspecies within a species. A mule is a mixture between a horse and a donkey. The result of this is usually infertile. That is what tilapia aquaculturists look for when they mix O niloticus and O. mozambicus. But its seems that several of those hybrids are somehow fertile. This is a good option. NO hormones, no GMOs. The main problem is getting broodstock that is 100% pure as almost all broodstock worldwide is somehow mixed.

    2) Sexual reversion is a process in tilapia culture in which tilapia fries are fed for 30 days with ground feed containing hormones. There are chemicals and natural hormones. And yes, there are a lot of controversy around how little is too much hormones. For what I can tell the use of hormones in tilapia fry has very little influence in the “transformation” of female tilapia into male. Instead of “transforming” the sex of tilapia, synthetic and natural male hormones make an atrophy of the female fry reproductive organs. On males it does not make a thing. So those “reversed” female tilapias when they are mature do not lay eggs and incubate them, so there is more time available to eat and if they eat more they gain more weight. There is a lot of controversy on the use of hormones, but up until now there is no ban on the use of it, but there is hint that avoiding hormones will be the trend in the future.

    3) There is a little confusion. Brucellosis and Mad cow disease are different diseases. Brucellosis is produced by a bacteria (Brucella abortus)meanwhile Mad Cow Disease or BSE (bovine spongiform encephalopathy) is a progressive neurological disorder of cattle that results from infection by an unusual transmissible agent called a prion. Different diseases, different symptoms, different origins.

    4) Up to my knowledge, there are no hormones or similar used in aquaculture feeds. If in doubt, please read the contents label of the feed bag to make sure. Yes, purina and cargill and several others sell feeds containing hormones, but those feeds are exclusively used in hatcheries for fry/fingerlings reversal. Those feeds are in a dust like powder and it is up to the aquaculturist to use them properly. Those feeds are not used during grow-out.

    5) Supermales. Those are an interesting mixture of high genetic technology and good Aquaculture management. The process to obtain a supermale is a little difficult to explain and this is not the objective of my note. What I can tell is that the offspring of Supermale tilapia (bred with no GM female) is always less efficient than their parents, but they are no hormone treated, that is the good part.

    As for the Cuban paper and the book you have written about, I cann’t make an opinion mainly because I have not read them.

    Just my two cents.

    Roberto

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