Farmed cod in Norway descends from wild local stocks. After a few generations of development, it is now feasible to control the quality of the brood stock. In cod farming, the eggs are collected from fish spawning in tanks. In the wild, the time of spawning is dependent on the length of the day. Hence spawning in cod farming can be timed using artificial light, thus ensuring a supply of eggs all year round.
High mortality in the larvae and early fry stage
One of the biggest challenges in intensive cod farming is high mortality in the larvae and early fry stage. In contrast to salmon, which are fed pellets from an early stage, the cod larvae are dependent on live feed after the yolk sac phase. Throughout the different larva stages, cod need prey of increasing size. Today, most cod fry are produced indoors where environmental factors such as temperature, light and water chemistry can be controlled. The living prey of the cod larva is also produced indoors and is added to the water together with algae or algae concentrate. This so-called “green water” improves the survival of the larva. The growth of cod larvae can be substantial, with body weight increases of up to 15% in a day. After some time, the larvae are adapted to pellets. The pellets used in cod farming are considerably leaner than those used in salmon farming.
After the larvae and early fry stage, the production of cod is very similar to the production of salmon. However, there are some differences between the species. Farmed cod will usually spawn at the age of two years and a weight of approximately two kilos. This is unfortunate, as the spawning leads to bad appetite and therefore slower growth. Furthermore, school behaviour is not so well developed in cod populations and the cod tend to swim along the net walls and bottom. When moved to sea, the chance of escapes is greater in cod farming as the cod seem more tempted by the outside world and tend to bite on the nets.