Photo: NOFIMA

Nofima Insights: Light and Feed Strategies for Salmon Aquaculture

NORWAY
Wednesday, March 19, 2025, 09:00 (GMT + 9)

Can light and feed manipulation effectively regulate sexual maturation in farmed salmon?

Vetle Skjold's doctoral research at Nofima explores this crucial question, offering potential solutions to enhance animal welfare and address industry challenges.

"It's remarkable how fundamental light is in controlling salmon's sexual maturation," says Skjold, now a Nofima researcher, following his commercially relevant doctoral thesis at the Norwegian University of Life Sciences (NMBU). His findings offer insights for land-based salmon smolt farmers grappling with premature sexual maturation.

Light as Nature's Calendar

Salmon naturally use daylight cues to synchronize developmental processes. Spring's increasing daylight signals smoltification in rivers and triggers spawning migration in mature salmon. However, continuous light, while optimizing aquaculture production, disrupts this natural rhythm.

"Depriving salmon of their natural circadian rhythm can have adverse effects, especially increased sexual maturation," Skjold explains.

Addressing Premature Puberty

Early sexual maturation in male salmon poses significant challenges, leading to physiological stress, growth cessation, and diminished fillet quality. Extending the land-based production phase, a strategy to mitigate sea lice issues, necessitates optimizing the on-land environment for sea-ready fish.

Research Findings: Light and Feed Interactions

Skjold's research examined the impact of various light regimes (continuous, simulated spring, and simulated autumn) on salmon growth and maturation in brackish and seawater environments.

• Light Regime Impacts:
  • Simulated spring light: High sexual maturation rates.
  • Continuous light: Moderate sexual maturation.
  • Simulated autumn light: Minimal sexual maturation.
• Feed Composition:
  • High-protein, low-fat feed reduced testicular growth and fat storage.
  • Salmon compensated for low dietary fat by synthesizing short-chain saturated fatty acids.
• Gene Expression:
  • Significant gene activity changes in the testes and pituitary gland of sexually mature salmon.
  • Identification of potential key genes regulating sexual maturation.

The fish in the experiment were first smoltified and then placed in tanks on land in brackish water at Nofima's research station at Sunndalsøra

These findings align with natural salmon reproductive patterns and reinforce previous research on smaller smolts.

Practical Recommendations for Aquaculture

Skjold offers practical advice for farmers extending land-based production:

• Implement falling or reduced day length after smoltification to mitigate sexual maturation and improve growth.
• Consider leaner feed during the post-smolt phase to reduce testicular growth and fat storage, while balancing potential negative impacts.

Vetle Skjold, 33, from Bergen, defended his thesis, "Sexual maturation, metabolism, and growth in Atlantic salmon: Effects of photoperiod and the ratio of protein to fat in the feed during post-smolt production," on February 27th at NMBU. His main supervisor was Bente Ruyter, with co-supervisors Jens-Erik Dessen, Kjell-Arne Rørvik, Lill Torunn Mydland, and Trine Ytrestøyl.

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