FARMED SALMON EXPERIENCE FASTER SEXUAL MATURATION AND HEALTH CHALLENGES IN WARMER WATERS

Farmed salmon experience faster sexual maturation and health challenges in warmer waters. Norway’s Institute of Marine Research scientists, investigated how water temperature can affect farmed salmon.

“We investigated how water temperature affects growth, sexual maturation and health in both ‘regular’ diploid and triploid Atlantic salmon,” says marine scientist Thomas Fraser. 

Triploid salmon are farmed fish that have been made sterile. They have three sets of chromosomes (triploidy) instead of two (diploidy).

Sexually mature salmon become sick more easily and grow less well, which is why sexual maturation is undesirable in farming.  

The advantage of triploid salmon is that female salmon avoid sexual maturation and thus grow faster compared to diploid salmon that mature.

But triploids may have poorer welfare.

Read more about the challenges and opportunities with sterile salmon.

Higher temperature leads to faster sexual maturation

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

The results show that sexual maturation is strongly temperature dependent.

“We saw that higher temperatures led to faster sexual maturation in diploid salmon. Both sexes matured faster, but males started at lower temperatures than females,” says Fraser.

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

“In males, sexual maturation first occurred at 8 °C, and at 18 °C or higher all were sexually mature,” says Fraser.

Among females, 76 percent were sexually mature at 20.5 °C.

In this experiment, no triploid female salmon reached sexual maturity.

Grows well at 10.5 °C

“We saw that 10.5 °C was the optimal temperature for growth for both diploid and triploid salmon, and the fish were then around 1.2 kg.

“When the temperature was above 10.5 °C, triploid salmon were generally larger.

“This is probably because the triploids could use all their energy on growth and did not need to spend any on reproduction, since they do not sexually mature,” says Fraser.

Clear health challenges at higher temperatures

Triploid salmon could have been a solution to avoid sexual maturation, but they show clear health problems in warmer waters.

“The eye disease cataract, which is when the lens is partially or completely opaque so that the fish eventually becomes blind, increased greatly 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 they 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 killed.

Reference

Fraser, TWK, Sambraus, F., Remø, SC, Stien, LH, Hansen, TJ, & Fjelldal, PG (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.

Photo: Pixabay

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