Prawn sex-change boosts male yields, say scientists

[October 19, 2015]  By Ori Lewis and Elana Ringler
 
 An Israeli-developed method to enhance prawn yields without resorting to genetic modification has started to take hold in Asia, the researcher who has developed the technology said.

Male prawns can grow up to 60 percent larger than females and a breakthrough by a team of researchers at Ben Gurion University in creating all-male prawn populations is significantly increasing income for farmers.

"This technology is using a cutting-edge scientific approach called temporal gene silencing through RNA interference and the idea is that if we use this technology we can produce an all male population that is for the benefit of the end user, the grower," Professor Amir Sagi, who heads the research group, told Reuters.

"The advantage of this technology is that with using all male with that technology is that we do not have to use any chemicals nor any hormones and it is a non-GMO, saying that it is not genetically modifying the organism."

The method involves carefully injecting females of the giant freshwater prawn known as "Macrobrachium rosenbergii" with a molecule that silences a gene. This changes the sex of a female and ensures that all its eggs hatch as males.

The sex change occurs only in the generation that has been injected and does not affect the offspring, Sagi explained.

"All male in this species that we are referring to are growing much faster than the females so if the end user, the grower, in India or in Vietnam or in China will grow those, he will have something like 60 percent increase in its income," Sagi said.

Delicate injection of the fluid that changes the sex of the females is administered by hand to each individual young prawn at a site in southern Israel before batches are shipped to growers in Asia.

Sagi said expert workers can inject as many as 2,000 prawns per day and as each individual can excrete thousands of eggs over several cycles, it can facilitate a population of millions in an industry of higher-end foods.

Israeli private firm Tiran Shipping, which has aquaculture interests in Asia, has invested in the technology and uses it to grow the prawns, Sagi said.

A Beersheba-based start-up called Enzootic established by the university and private investors focuses its research on developing prawns with the technology but academic research into additional applications is ongoing.

It has yielded a tool to fight against bilharzia in Africa, doctoral student Amit Alkalay Savaya, who works in Senegal, said.

"The prawns that we are researching here in the lab are the native predators of the snails (that cause bilharzia) so we are trying to use the prawns as biological controlled agents over the snails," he said.

Sagi said it was recently discovered that prawn teeth contain enamel, and although research is still in its infancy, this could have implications in dental care advances.

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