Cold water results in fewer males says new findings from Norway –

Cold water results in fewer males says new findings from Norway Published:  18 January, 2006

PROGRESS in halibut research has been reported from Norway.

Solveig van Nes of Norway’s Institute of Aquaculture Research AKVAFORSK is claimed to have found one of the key factors that influences the sexual development of halibut larvae. Since females grow significantly larger than males, farmers are now said to be able to direct their production toward fewer males and higher profits. The method is simple: Use the same temperature as the ocean!

Ms van Nes is to present her research findings in her doctoral dissertation, which she will defend at the Norwegian University of Life Sciences (UMB) on Friday.

Halibut is a product in high demand, especially female halibut since they become much larger than their male counterparts. Because of the favourable characteristics of the female halibut, van Nes wanted to find a method of increasing the number of farmed females. The sexual development of fish larvae in several different species appears to be sensitive to temperature. It was therefore interesting to investigate whether the sexual development of farmed halibut was also affected by temperature. In the wild, halibut larvae live at a temperature of 5-7° C, whereas in fisheries the temperature is 11-13° C. The advantage of the high temperature is that it accelerates the growth of the larvae, which then develop more quickly through the demanding larva stage and into a more robust stage.

In her research, van Nes found that increasing water temperature in the larva stage resulted in a larger number of males. At a temperature of 13° C during the larva stage, 62 per cent of the larvae developed into males. She also examined several genes that are involved in sexual development, and successfully isolated two aromatase genes responsible for the production of the female hormone oestrogen. One of these genes proved to be particularly sensitive to temperature, thus hampering oestrogen production at high temperatures. This is the reason for the large number of males that develop at 13° C. In contrast, this aromatase gene is more active in cold water, causing more halibut larvae to develop into females so that the proportion of males to females is close to 50-50.

van Nes is not surprised that it is the natural temperature that provides the best conditions for the sexual distribution of fish since this is also true for several different species. “However, it is not always easy to evaluate the effects of temperature on important characteristics during production. If we conduct more research in this field, we will have a basis for re-evaluating the optimal temperature for halibut,” explains the doctoral candidate.

Solveig van Nes is to defend her doctoral dissertation on Friday, 20 January 2006. The title of her lecture is “Applications of research of sex determination in aquaculture”. is published by Special Publications. Special Publications also publish European Fish Trader, Fishing Monthly, Fish Farming Today, Fish Farmer, the Fish Industry Yearbook, the Scottish Seafood Processors Federation Diary, the Fish Farmer Handbook and a range of wallplanners.