Experiments to achieve sterile cod have been unsuccessful. (Photo: Frank Gregersen, Nofima)

Aquaculture researchers work to develop sterile fish

NORWAY
Thursday, June 28, 2012, 01:10 (GMT + 9)

The aquaculture industry is looking to raise sterile fish to keep them from spending energy on sexual maturation. Sterile fish would also not be able to reproduce with wild fish if they escape their pens and swim into the ocean.

Øivind Andersen at Nofima Mat, the Norwegian Institute of Food, Fisheries and Aquaculture Research, is researching how to tackle the problems associated with fish reaching sexual maturity before they reach their slaughter weight.

The new technique entails injecting antibodies into sexually mature female fish to keep her offspring from maturing sexually. This method is still in its initial experimental stages, Science Nordic reports.

“The fish expend an enormous amount of energy developing gonads and after a while they also stop eating because they think they are on a journey to spawning grounds," Andersen explained. “Female fish fill up with roe, because they don’t get the stimuli they need to spawn.”

The aquaculture industry has already managed to raise fast-growing salmon that reach slaughter weight before sexual maturation.

Experiments with cod have not been as successful, however.

“As for cod, all the males and many of the females are sexually mature at age two, long before reaching slaughter weight. It’s really inefficient, giving them lots of feed that simply gets converted into developing gonads during their sexual maturation,” he explained.

Developing triploid fish is one of the techniques currently in the works: the roe is subjected to a pressure shock so the eggs get three pairs of chromosomes instead of the normal two. This sterilizes the female salmon only, however.

Problems with this method include that producers worry consumers will reject fish that have manipulated chromosomes and that the technique causes deformations in many of the fish; still, several countries, including Scotland, market triploid fish.

Together with senior researcher Helge Tveiten, Andersen is now working on a new technique that sterilises farmed fish by vaccinating those that are ready to spawn but before they release their roe. The vaccine carries antibodies that block germ cells from turning into gonad cells.

While researchers have injected antibodies into cod roe, this technique is impractical for aquaculture, as it is tricky and time-consuming to inject anything into all the eggs of a fish. However, the antibodies can also be transferred from the mother fish to her roe so that the next generation is sterile. Thus, researchers want to vaccinate the mother instead of all her eggs.

“We’re attempting to develop specific antibodies which so far have been injected into salmon fry and triggering them to start producing these substances themselves,” Andersen added. “These fish do just fine and the response is there so now we’ll attempt to do it a generation earlier. In this way, the mother fish can produce hundreds of thousands of sterile fish.”

By Natalia Real
editorial@fis.com
www.fis.com

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