Previously, farmed cod in the Norwegian breeding programme could spawn three times before reaching harvest weight. After being selected for growth, they spawn once.
For six generations, Nofima’s breeding goal has mainly been growth. But breeding for growth has also reduced the number of cod spawnings during the 20 months at sea before slaughter weight from three down to one.
While it is a prerequisite that cod spawn in a breeding programme, spawning is an undesirable trait in commercial farming, as it limits the growth of the fish and increases the risk of fertilised eggs spreading in the sea to cross with wild fish. Therefore, Nofima wants to put an end to early sexual maturation.
Recently, Nofima’s breeding scientist Anne Kettunen led a major trial. She tested the extent of early sexual maturation on more than a hundred full-sibling families in net-pens in Nordland. The study showed that 84% of females and 91% of males reached sexual maturity at two years of age when they were not managed with light. Calculations show that there is considerable genetic variation in early sexual maturation in cod, with 33% of the trait dependent on genes and the rest on the environment.
“This means that it is possible to breed for lower frequency of early sexual maturation, and thus further reduce the risk of spawning in net-pens. In Nofima’s breeding work, we are looking for several solutions, where breeding is one of them. Of course, production management at the fish farms is also part of the solution,” said Kettunen in a press release.