Background
Mortality in sea of Norwegian salmon production is 14% (Fiskehelserapporten 2025 - Veterin��rinstituttet), whereas the Norwegian authorities aim for 5%. One way to reach this goal is to ensure that the smolt that are set out in the sea are of high quality. The aim of this study was to estimate the effects of early-life RAS rearing, genetics, and dietary fat levels on performance and health of A. salmon before and after sea transfer.
Material and Methods
A feed trial with triplicate RAS tanks with two diets (six tanks in total) was performed at the Nofima Research Station for Aquaculture. Fish (ca 1700 fish in total) came from 70 families from Benchmark Genetics including two extreme groups with high (HIGH) and low (LOW) breeding value for fillet fat. Two feeds with different fat levels were produced at Skretting's feed technology plant (Skretting Aquaculture Innovation, Stavanger, Norway). At size 150g, records were obtained for survival, growth, length, condition factor (CF) and external welfare on all fish (including cataract recorded using visual inspection). From 30 fish per extreme groups, hepatosomatic index (HSI) and visceral somatic index (VSI), nephrocalcinoses (0/1) were also recorded. The fish were later transferred to sea cages and fed one feed until slaughter at 750g. The same traits will then be recorded plus fat content of liver and NQC and visceral somatic index. A second sample from the extreme groups were recorded as above at this life stage. All fish were genotyped using an array of Benchmark Genetics containing 70k SNP markers.
Results and Discussion
Before sea transfer fish show significantly higher HSI for the extreme HIGH genetic group compared to the LOW genetic group (1.52 vs 1.36%) and significantly higher HSI in fish fed the highest dietary lipid level (1.51 vs 1.37%). The interaction between genetic group and feed spanned from 1.27 to 1.6%. For VSI, these figures were 8.0 and 7.6% for the genetic group effects and 8.0 and 7.6% for the feed. The interaction between genetic groups and feeds spanned from 7.3 to 8.2g. There was overall high incidence of skin lesions (13.9%), opercular shortening (6.0%) and cataract (55%). There were small differences in production traits between the feeds (Feed Conversion Ratio (0.75 and 0.77, p=0.07) for high and low fat diets, Specific Growth Rate (1.41 and 1.37, p=0.05) and Thermal Growth Coefficient (2.00 and 2.07, p=0.07). Final results come in May.
Acknowledgment
This project has received funding from the European Union's Horizon Europe Research and Innovation Actions programme under grant agreement N° 101181159.