The water temperature suitable for salmon growth is 13-17°C for freshwater and 11-16°C for saltwater. If the water temperature is too low, they will lose their appetite, but salmon are cold-water fish and are relatively tolerant of low water temperatures. On the other hand, it is sensitive to high water temperatures, and growth becomes difficult when the water temperature exceeds 20°C. Therefore, global warming will result in a narrowing of the area where salmon can grow.

Various factors affect growth. For example, an oxygen concentration of 6-10 mg/L is optimal. Salmon absorb oxygen to digest their food, so if oxygen levels are low, food digestion will not proceed, leading to worsening FCR. Too much carbon dioxide also worsens FCR and even leads to die-offs. There is no problem for less. In addition, ammonia nitrogen and nitrite nitrogen are toxic to salmon.

Salmon are farmed in freshwater for one to two years before being transferred to ocean fish ponds. In the stage of transition from freshwater to seawater, the salinity is gradually increased from freshwater to acclimate to the salinity of seawater. In Japan, this process takes about half a day. This is called acclimation. Fry that do not acclimate well to seawater during acclimation die or stop eating food altogether and do not grow. So, the skill of this acclimation process has a very significant impact on the productivity of aquaculture.

Salmon blood has a salt concentration of just over 1%. In contrast, the salinity of seawater is about 1.25-1.5% in the Danish sea and a little over 3% in the Japanese sea. Salmon in sea-surface fish tanks maintain their internal environment by expelling salt from their bodies to adjust for the difference in salinity between their bodies and the seawater. This is called osmoregulation. There is not much difference between the salinity of the Danish sea and the salinity of the salmon's blood. Therefore, the need for osmoregulation is relatively small for Danish salmon. Osmoregulation is stressful for salmon. One of the reasons for the large difference in FCR (Feed conversion ratio) between Japan Salmon Farm and its Danish subsidiary may be this difference in stress.