Study points to lower phosphorus requirements in net-pen salmon.
A new study led by researchers at the Institute of Marine Research (IMR) in Norway suggests that phosphorus (P) levels in commercial salmon feed could be reduced without compromising bone health or growth performance during the sea-cage grow-out phase.
The research, conducted in collaboration with Ghent University, Mowi Feed and other partners, assessed Atlantic salmon reared in sea cages from 1.8 kg to 4.2 kg under natural seasonal conditions between December 2022 and July 2023. Fish were fed diets containing increasing levels of total phosphorus ranging from 6.1 to 11.2 g/kg.
The study found that adequate bone mineralisation, mechanical strength and normal growth could be maintained at lower available phosphorus levels than those typically used in commercial feeds. Fish required 3.7 g/kg available P during colder months with slower growth, rising to 4.6 g/kg during warmer periods with faster growth.
Vertebral deformities were not affected by dietary phosphorus levels across the trial, while digestibility and growth rates increased with higher temperatures later in the production cycle.
The findings indicate that total dietary phosphorus content could be reduced by 16–24% compared to current commercial formulations, with potential cost savings and lower environmental emissions.
Phosphorus is a key nutrient in salmon diets but is both a limited and costly resource. Excess phosphorus is excreted by fish and contributes to nutrient discharge from sea-cage farming, increasing the risk of eutrophication.
The study highlights the importance of aligning phosphorus inclusion with seasonal growth conditions and improving nutrient efficiency in feed formulations.