Scientists at Nofima have a number of practical tips that can help fish farmers improve the smolt’s robustness and reduce losses at sea. Photo: Terje Aamodt/Nofima

Project Year 2016

Swimming for dear life!

 Fish health    Production biology  

Mortality after transfer to the sea can be prevented at the pre-stocking stage, if fish farmers make a few simple changes.

In 2015 some 41 million salmon died after transfer to the sea in the Norwegian salmon farming sector, according to unofficial figures.

“However, with a few simple changes many of the salmon that die in pens could probably survive and grow to become good food and yield higher profits for the farmers,” says Sven Martin Jørgensen, scientist and project manager of the FitSmolt project.

Unfit smolt are more susceptible to disease and more sensitive to handling and stress. By improving the overall health of young fish, farmers will have better quality smolt to work with that are better able to withstand the tougher conditions in the sea.

Here are two changes that research has shown are effective.

1: Remove the poorest swimmers

The scientists developed a test to rank the swimming capabilities of salmon parr. The weakest swimmers were found to have poorer cardiac health and shorter gill lamellae than the best swimmers.

The scientists found the same differences over eight months later, and the best swimmers had grown 5–8% more and had significantly fewer ulcerations on their fins than the poorest swimmers.

By removing the poorest swimmers at an early stage, the farmers will be left with smolt with both better growth potential and stronger organs for oxygen transport, i.e. more robust smolt.

2: Exercise

Exercise improves the salmon’s growth, ensures they develop stronger heart and swimming muscles, and increases their physiological capacity.

In the FitSmolt project, the scientists exercised the salmon from the fry stage. The positive effects of exercise were obvious: better growth, a stronger heart and physiology, and a significantly higher survival rate under PDinfection experiments.

“If more fish farmers employed the methods described above, we should see significant, permanent reductions in mortality rates in the coming years,” says Jørgensen. “We owe it to the salmon!”

The Research Council of Norway (NFR) and the Fishery and Aquaculture Industry Research Fund (FHF)

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