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August 30, 2013
Geneticist Roger Doyle on EMS/AHPNS and Inbreeding
In Thailand, on May 31, 2013, Dr. Roger Doyle, CEO of Genetic Computation, Ltd., and a retired professor of biology from Canada’s Dalhousie University, gave a 36-minute, oral presentation on the relationship between inbreeding and diseases like EMS/AHPNS. Here, I’ve transcribed his introductory comments. To hear his full presentation, Click Here.
Dr. Roger Doyle: You probably know about the EMS/AHPNS disease problem here in Thailand and in China, Malaysia and Vietnam. Over the last couple of decades, world shrimp production increased every year until 2010, and then in 2011, it fell. In 2012, it fell again, and in 2013, I’ve been told that it’s a disaster here in Thailand. I’m going to look at this disease from the point of view of a geneticist and evolutionary biologist. Thus far most of those who have been trying to solve this problem have been microbiologists. I’m going to present a different point of view on this disease and look at it as an inbreeding problem.
Shrimp breeders have broodstock that they’ve collected at great expense. They take great pride in maintaining its genetic quality by keeping inbreeding at a low level while selecting for rapid growth and high survival. They are quite good at what they do.
Normally, a very small fraction of the breeder’s gene line gets sent to hatcheries. Breeders sell their very best families, the families that genetic analysis predicts will be the most productive in hatcheries and on farms. Usually, it’s just the offspring from a couple of families. All the male parents are brothers and all the female parents are sisters. There are several reasons for doing this. One reason is to make sure that the PLs have absolutely zero inbreeding. Usually they are hybrids of two families that are as distantly related as possible. Another reason is to make sure that the PLs are as uniform as possible. The third reason is to protect their investment. If farmers grow the animals to maturity and then breed them, the offspring from the second generation will be inbred and not perform well.
Here in Thailand, as many as sixty percent of the farmers are purchasing PLs that were produced from farm grown, second-generation broodstock. In fact, the copying goes on and on through several generations, and the offspring get weaker and weaker and more susceptible to disease with each new generation. I have some information from a shrimp breeder in Mexico, Farallon Aquaculture that supports this hypothesis. Farallon select and produces good quality PLs that are widely copied and reproduced by farms and hatcheries. In 2012, the government of Mexico surveyed farms that used farm-grown broodstock and broodstock that came directly from the shrimp breeder. In the chart (below), the orange bars show how much better the yield is with the PLs that came directly from the breeder (the non-inbreed stock), compared to the blue bars that represent the copied stock. The survey was done in the state of Sinaloa on the northwest coast of Mexico, where there’s a big whitespot problem.
Now I want to talk about inbreeding and its affect on survival. Actually, there is very little information about that on shrimp, so I’m going use examples from other animals.
Shrimp News: For the remainder of his presentation, which is actually the bulk or his presentation, Doyle provides examples of how inbreeding results in increased disease susceptibility in other species.
Information: Genetic Computation Limited, 1-4630 Lochside Drive, Victoria, British Columbia Canada (phone 1- 250-727-7945, fax 1- 250-727-7984, email firstname.lastname@example.org, webpage http://www.genecomp.com/Roger_Doyle.htm).
Source: Network of Aquaculture Centres in Asia-Pacific (NACA) Webpage. Soundtracts: Artisanal Tropical Aquaculture in a Genetic Plunge Towards Extinction. Dr. Roger Doyle. May 31, 2013.
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