A Norwegian research project has been assessing the interplay between nutrients in salmon feed to achieve optimal growth, robust health, and high-quality fillets.
Over the past decades, fish oil has been gradually replaced with vegetable oil in aquafeed. During this time, the salmon's requirement for saturated fat has not received sufficient attention.
“Saturated fat has a greater impact on fillet quality than previously thought. Fishmeal and fish oil have a unique composition of omega-3 fatty acids, saturated fats, and cholesterol. It is therefore important to assess what these changes mean for the quality of salmon raised on today’s plant-dominated feed”, said Nofima scientist Nini Sissener.
Sissener carried out a study at the Institute of Marine Research and found that frozen salmon fillets lost more liquid during thawing when sourced from fish that had received insufficient saturated fat during the growth phase. Additionally, a low cholesterol level in the feed reduced the fillet’s firmness and red coloration.
Juvenile salmon require sufficient zinc and omega-3
Scientists have also investigated how zinc levels impact health and resilience in small salmon during their freshwater stage. High levels of zinc and omega-3s have positive effects on scale development, wound healing in the skin, increased bone density, and overall growth.
“Together with omega-3, zinc enhances skin health, and more omega-3 improves the utilization of zinc. They are truly a powerful duo in salmon feed and act synergistically,” said Bente Ruyter, senior scientist at Nofima.
For robust growth under optimal conditions in land-based tanks, research indicates that a 6% omega-3 content in total fatty acids in the feed is sufficient.
Salmon in the sea require more
Trials were also conducted on larger salmon in sea cages, where scientists found that fish lost minerals and had lower harvest weights when fed diets with low zinc content. However, mineralization improved when omega-3s in the feed increased, and total fat levels decreased.
Ten years ago, omega-3 levels in Norwegian salmon feed were lower than they are today. When earlier research showed that salmon needed more omega-3, the industry quickly adjusted the feed composition. Research from this project shows that salmon raised under challenging conditions in sea cages require more omega-3 for optimal growth, health, and fillet quality than those kept under ideal conditions in land-based tanks.
For example, salmon that received 11% omega-3 of total fatty acids in the feed resumed feeding more quickly after delousing than those fed 6.5%. Since feed intake typically drops after delousing, Ruyter emphasizes that a rapid return to feeding is essential.
Nutrient interactions are highly significant
“What’s exciting about these findings is that the interaction between nutrients plays a key role in skin health, red coloration, energy metabolism, membrane fluidity, and the salmon’s ability to adapt to new production environments," said Ruyter.
"Today’s production involves various technical solutions, warmer seas, and more sea lice. To thrive through the production cycle with good growth, health, and fillet quality, salmon need the right feed," Ruyter concluded.
The research project has been funded by FHF – the Norwegian Seafood Research Fund, and led by Nofima. Project partners included the Institute of Marine Research, Norwegian University of Life Sciences (NMBU), the Arctic University of Norway (UiT), the National Research Institute for Agriculture, Food and Environment (INRAE), the University of Gothenburg, Skretting Aquaculture Innovation AS, and BioMar.
