Cod holds an important place in European gastronomy. In spite of supply difficulties arising from the depletion of certain wild stocks, demand is still high. Cod farming therefore appears as an attractive business opportunity. Norwegian scientists studied cod farming in the 1980s. In parallel, Norwegian salmon farmers, looking for ways to diversify their activity, started fattening wild cod caught at sea, and thus helped refine feeding techniques. It was not until 2000, however, with the first production of young fish in hatcheries, that cod farming really took off, mainly in Norway. The activity first emerged, however, with varying degrees of success, in Scotland and Ireland, where salmon farmers took advantage of the similar fattening techniques used for the two species.
Latin name – Gadus morhua
Production (EU-27) – 2 560 t (2007); 21 % of global production.
Value (EU-27) – EUR 9.2 million (2007).
Main EU producer countries – Ireland, United Kingdom.
Main producer countries worldwide – Norway, Iceland, Ireland, United Kingdom.
Cod are reproduced in hatcheries with broodstock caught at sea. Males and females are placed in the same tank. The reproduction cycle is artificially created through photomanipulation, a technique that consists of inducing the species’ seasonal sexual behaviour by varying the length of artificial ‘sunlight’. This technique offers the advantage of producing eggs and fish all year long.
The eggs are fertilized naturally by the male and harvested on the surface of the spawning tank. They are placed in an incubator containing sea water kept at a temperature of around 5 °C with an ascending current. The eggs hatch in 12 to 14 days.
In nature, the female releases a million eggs which have a very low survival rate due to predation by other species, cannibalism, the fry’s specific diet and sensitivity to infections, marine currents, water quality, water temperature (which differs in terms of the stage of development), etc. Thus the challenge of cod rearing is to reach a level of technical sophistication that can mitigate the impact of these parameters to achieve an industrially acceptable survival rate.
Rearing of larvae – Three or four days after hatching, the larvae (0.2 mg) have consumed their yolk sac and are transferred to ‘first feeding’ tanks of sea water maintained at 11 °C with a continuous current. They feed on rotifera (a microscopic zooplankton produced in the hatchery) for around two months until they reach a weight of 0.2 g.
The nursery – The fry are then transferred to larger tanks that also provide a continuous current of sea water. They are gradually weaned, over a period of roughly two months, onto an inert protein-rich feed in the form of a very fine powder mixture (sometimes also with artemia produced in the hatchery). They are also vaccinated, especially against vibriosis, a cause of high mortality in this species. From this stage, a mechanical process constantly sorts the young cod, which are separated by weight (grading), because the bigger fish tend to eat the smaller ones.
Juvenile growth – When the fry weigh 2 g they are moved to large tanks where they feed on pellets of fishmeal and fish oil as well as vegetable protein supplements. At around 30-40 g, they are vaccinated by injection against bacterial infections. The grading process continues to limit mortality from cannibalism. The young cod remain in these large tanks for five to ten months, the time it takes to reach a weight of 50 to 200 g. The weight at which they are transferred to cages depends on water temperature, the season, the size of the cage, net mesh size, etc.
Cod are fattened in floating cages like those used for salmon, or in land-based tanks fitted with a recirculation system. The feed is pellets of fishmeal and fish oil and vegetable extracts. The fish are harvested and slaughtered when they reach a weight of 3 to 4 kg, i.e. after around two years of fattening.
Once slaughtered, the cod are delivered to a processing unit which sells them fresh, cleaned and cut up. Cod farming has developed in Norway, where a number of salmon breeders have moved into this market using various methods: sea cages, land-based tanks, normal, organic, etc. The activity is being developed in Iceland, the Faeroe Islands and Canada.
In the European Union, a large-scale experiment conducted in the Shetland Islands (United Kingdom) ended in financial failure in 2008. Fresh attempts are under way in Ireland and Scotland. The future of this activity depends to a large extent on the evolution of cod supply from North Atlantic and Arctic fisheries.