Ph.D. on ultrasonic screening of sex and maturation of salmon

On the 7th February 2020, Ingun Næve defended her Ph.D. on the development of ultrasound as a gentle method for sorting salmon parr and monitoring of maturation. This is an industrial Ph.D. that was carried out in a collaboration between NTNU and AquaGen.

Ingun Næve with a salmon, while doing sampling and evaluation of broodstock candidates in AquaGen.

AquaGen has already been applying these methods and tools in their production, and it gives an important contribution towards better fish health in the production of salmon broodstock. The title of the Ph.D. is “Development of non-invasive methods using ultrasound in the monitoring of Atlantic Salmon (Salmo salar) production and reproduction”. The main supervisor has been professor Elin Kjørsvik from NTNU (Norwegian University of Science and Technology), and the assistant supervisor has been senior scientists Maren Mommens from AquaGen.

Gender sorting of parr

During the freshwater farming of parr, a method of gender identification (from 50 g body weight) was developed using ultrasound technology. An ultrasound probe, with up to 97% correct gender identification, was identified. It was also discovered that the parr had exceptional good tolerance for the procedure. This procedure eliminates the need for handling of the broodstock for gender identification in the seawater phase, this again reduces stress related to handling and risk of escapes.

Gender sorting of parr can also be used to utilise the different potential of growth for female and male fish in food production. In general, male fish are faster growing than female fish when they are in the same groups. We have seen in gender assigned groups, that both male and female fish have better growth. Also, female fish have better utilisation of the fillet than male fish, therefore it is possible to increase the biomass through gender sorting.

Monitoring of maturation

To monitor the development of maturation, several methods were developed, for example, a gentle method for the estimation of gonadosomatic index (GSI) for both male and female fish. This method eliminates the need for killing the breeding candidates or the need for being dependent on dead fish for the monitoring of maturation. Furthermore, the US-GSI-method can be used to identify female fish that is expected to mature early and late in the stripping season.

In the weeks leading up to the eggs being released into the abdominal cavity, changes in the eggs observed in ultrasound images can be used to predict maturation time. Using US-GSI, one can distinguish between female fish that are expected to mature early and late, and the number of female fish to be handled that is expected to mature late can be reduced. This brood management procedure can potentially reduce the number of handling of female fish during a period when they are sensitive to the effects of stress on reproduction.

Reduction of handling

Ultrasound examination on salmon.

The ultrasound methods, that are developed here, can be used to establish a surveillance system which reduces the handling of the salmon throughout their life. With this system, we can optimise the production planning and simplify the logistics around the handling of the broodstock. These results are inspiring for the further work on developing and enabling the methods for monitoring of maturation of salmon and other commercial species, such as rainbow trout, Pacific salmon (Coho) and lumpfish, with the use of ultrasound.

The newly acquired knowledge from this Ph.D. is groundbreaking research and is already being used for the production in AquaGen. Ingun is now hired as a senior scientist and will continue to work within this and other fields in the company.