A researcher at Nofima has uncovered important insights into how light and diet can be used to control the maturation of farmed salmon.
Vetle Skjold’s doctoral research at the Norwegian University of Life Sciences addresses a major issue in the aquaculture industry: early maturation in male salmon, which can harm fish welfare and production quality.
In the wild, salmon use changes in day length as a natural cue to synchronise key biological processes. In aquaculture, continuous light is often used to optimise production, but Skjold’s research suggests this may disrupt the salmon’s natural circadian rhythm and lead to premature maturation.
“We deprive the salmon of its natural circadian rhythm, and this can be negative, especially if it leads to increased maturation,” said Skjold.
When salmon mature prematurely in brackish water, they begin adapting to freshwater conditions, which negatively impacts their health and growth and can even lead to death. Additionally, mature salmon stop eating, resulting in poor growth and quality issues, such as pale fillet colour.
Keep it natural
Skjold and his team tested different light regimes – spring-like increasing day length, autumn-like decreasing day length, and continuous light – on large salmon smolt raised in brackish water. The results revealed that spring-like light led to high maturation rates, continuous light resulted in moderate maturation, while autumn-like light minimised maturation.
“This aligns well with the salmon’s natural reproductive strategy,” said Skjold.
“In spring, maturation is initiated, while autumn is a period for either spawning or building energy reserves to prepare for spawning the following year. Continuous light, on the other hand, seems to facilitate early maturation after smoltification, although the exposure does not involve changes in light signals to the fish.”
Skjold also investigated the effects of diet on maturation. Lower-fat, high-protein diets were found to reduce testicular growth, potentially offering another tool for controlling maturation in farmed salmon.
The research has potential to transform the aquaculture industry beyond its initial findings.
“These feed and light regimes may also be relevant for post-smolt production in facilities using recirculating aquaculture systems, even though the first part of the experiment was conducted using flow-through system,” said Jens-Erik Dessen, one of Skjold’s supervisors.
