When salmon are exposed in open cages in the sea, they face a changing environment, disease and sea lice. Many small salmon smolts are not sufficiently robust to deal with these threats.
This is one part of the problem that scientists and the aquaculture industry have been closely working together to solve for the past three years. They have discovered that it is possible to reduce the time that the salmon spend in the sea by increasing the time on land, or in closed facilities in the sea. The scientists have also investigated the consequences for the performance, physiology and production costs of the fish.
What are Postsmolts?
Smolts are salmon that weigh around 80g and have undergone smoltification. The smoltification process involves major physiological and morphological changes for the fish, such that they are able to tolerate life in salt water. The term “postsmolt” is used to describe the fish from the time it has acquired sea water tolerance and the initial part of the growth phase in salt water.
Protected Until Young Adults
“We have achieved 99 per cent survival in repeated experiments using our method, in which the fish are not transferred to cages in sea until they are postsmolts. The results show that some fish cannot cope with the transfer from land-based facilities to the sea if this is carried out when they are immature. It is exactly these fish that are more robust, and can cope with the stress that they experience in the sea when they are instead transferred as young adults, weighing well over 250g,” said Senior scientist Bendik Fyhn Terjesen, a Nofima technical project leader in “Optimised postsmolt production” (OPP), which is supported by the Research Council of Norway.
The project is a collaboration with several R&D institutes and stake holders in the aquaculture industry (listed below). Even though the fish from a particular facility can occasionally achieve very high survival after transferring smolts weighing around 80g, we have not until now had systematic knowledge about what is needed to ensure high survival rates over time.
Less Salt, More Exercise
The project group believed that in addition to allowing the smolts to grow more than usual before being set out into the sea, the salinity of the water and the water velocity in the tank, would be crucial factors in increasing survival. After experiments with various combinations and using large-scale experiments, Fyhn Terjesen and his colleagues carried out an experiment in a recirculation plant using the solution that the project group believed would be the best. The solution involved, among other things, a lower salinity of the water, exercise, and gentle handling of the fish in the closed facility on land, right up until the salmon weighed 600 g. The fish were subsequently transferred to normal cages in the sea. When the salmon had reached 2.5 kg, 99 per cent survived.
Sigurd Handeland at Uni Research has the same experience from other experiments in the OPP project. He did an experiment with fish that were kept to1 kilo in a semi-closed containment system in the sea, and obtained similar results as Fyhn Terjesen obtained on land.
“We have investigated salmon in the semi-closed system in the sea, operated by Marine Harvest. Survival of fish up to a weight of 1 kg was 99.2 per cent,” said Handeland.
“In addition, it took four-six weeks less time for the fish to reach one kg, compared with the reference group in a traditional facility.”
Robustness
The scientists working in the OPP project have also shown that keeping young salmon longer in closed facilities gives better control of the production, which is beneficial for the fish.
“We believe that our results provide a basis to recommend continuing to hold the salmon in closed facilities with full control of the water quality and not disturbing the fish until they are postsmolts, weighing well over 250 g. They are significantly more robust at this weight than they are at 80 g, and more will survive in the sea,” said Fyhn Terjesen.
“It will be more difficult in everyday aquaculture to achieve the 99 per cent survival that we achieved in our carefully monitored experiments. But we have shown that the potential is there. What remains is to develop innovative solutions in technology and biology in order to get results that can be seen in statistics from the aquaculture industry,” said Fyhn Terjesen.
A Conference on Closed Containment Aquacultuture
The results from OPP were presented at the “Smolt production in the future” conference organised by Nofima and Sunndal Næringsselskap at Sunndalsøra in October. The level of participation this year was the best ever, with over 200 delegates. It was a general feeling among the industrial stakeholders that several new facilities will be dimensioned to have recirculation systems or will be semi-closed containment systems in sea, for the culture of larger fish before they are transferred out to cages. There are, however, several challenges to meet.
Innovations will be required within technology, sensor technology, water quality, documentation of fish welfare and how disease is to be avoided or combated when it occurs in closed containment systems.
“We want to continue research into culture of postsmolts in closed systems, in order to contribute to solving the challenges that are limiting growth in salmon production, up to 2050,” concluded Mr Terjesen.
