Farmed salmon matures faster and has more health problems in warmer water

– We examined how water temperature influences growth, maturation, and health in both "regular" diploid and “sterile” triploid Atlantic salmon, says marine scientist Thomas Fraser.

Mature salmon  are more susceptible to disease and grow slowly, making maturation undesirable in aquaculture.

The advantage of triploid salmon is that the females do not mature and so they outgrow maturing diploid salmon.

However, triploid salmon may have poorer welfare.

Read more about the challenges and opportunities with sterile salmon.

Higher temperatures lead to faster maturation

The experiment was conducted in seawater over a period of 140 days, where salmon were divided into groups and exposed to different temperatures ranging from 3.0°C to 20.5°C.

The results show that maturation is highly impacted by the water temperature.

– We observed that higher temperatures led to earlier maturation in diploid salmon. Both sexes matured earlier, but males began maturing at lower temperatures than females, says Fraser.

No fish matured at temperatures of 5.5°C or lower.

– In males, maturation first occurred at 8°C, and at 18°C or higher, all had matured, Fraser explains.

Among females, 76% were mature at 20.5°C.

In this experiment no triploid females matured.

Optimal growth at 10.5°C

– We found that 10.5°C was the optimal temperature for growth in both diploid and triploid salmon, with fish reaching around 1.2 kg.

At temperatures above 10.5°C, triploid salmon were generally larger.

– We believe this is because, unlike diploid salmon, triploid salmon use all their energy for growth rather than reproduction since they do not mature, says Fraser.

Triploid salmon could potentially be used as an alternative to prevent maturation, but they also present challenges.

Clear health challenges at higher temperatures

Health problems became more apparent in warmer water, especially in triploid salmon.

– The eye disease cataracts, where the lens becomes partially or completely opaque, increased significantly in both diploid and triploid salmon but was more severe in triploid salmon, says Fraser.

Cataracts became more common in triploid salmon at temperatures above 5.5°C, while it increased in diploid salmon only above 15.5°C.

At temperatures above 20.5°C, the eye disease in triploid salmon became so severe that the fish had to be euthanized. 

Reference

Fraser, T. W. K., Sambraus, F., Remø, S. C., Stien, L. H., Hansen, T. J., & Fjelldal, P. G. (2025). Growth, sexual maturation, cataracts, and blood biochemistry in diploid and triploid Atlantic salmon post-smolts reared at one of eight constant temperatures from 3.0 to 20.5 °C for 140 days. Aquaculture, 602, 742323.