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Marine Science



Cod sex gene identified by using a tiny DNA sample,  making it possible to determine both the sex of the fish and whether it is a coastal cod or skrei (from the Barents Sea).

The breakthrough was recently made by scientists from CIGENE (at the Norwegian University of Life Sciences – NMBU) and Nofima.

Previously, the sex of cod could only be determined in adult fish displaying either eggs or milt. Now it is possible to find out whether a cod is female or male at any time in the fish’s life, right from when it is a fertilized egg. The same DNA sample will also reveal whether it belong to the Norwegian coastal cod population or the skrei population living in the Barents Sea. This marks an important milestone in fish research of importance for the management of the wild cod stocks, and also for investigating the impact of pollution and temperature changes on the Norwegian national fish.

“This research will also have a great impact on future cod farming,” says Øivind Andersen, a senior scientist at Nofima.

Early sexual maturation in male cod has been a major challenge for the aquaculture industry. For this reason, fish farmers only want to produce female cod, which mature much later than males. Now females can be distinguished from males at a very early stage of development, thus profits can be increased significantly once cod farming gets going again.

The hunt for the sex gene in cod has been going on for several years through the Aquagenom project, within the BIOTEK2021 programme financed by the Research Council of Norway. In addition, the Norwegian cod breeding programme has provided data for the research work.

Øivind Andersen explains that the work has been very complicated, as different genes govern sexual development in different fish species.

“We also had to resequence the whole cod genome to identify the region that distinguishes males and females,” says Andersen.

The breakthrough in the joint project between CIGENE at the Norwegian University of Life Sciences (NMBU) and Nofima also means it is now possible to determine the sex of related codfishes.

“For example, this tool can be used in the current studies of whiting and effects of oil pollution. It will also be important in ongoing research on how climate change affects sexual development and reproduction of polar cod in the Barents Sea,” says Andersen.