Validation and Genetic Parameters of the X-ray Method for Phenotyping Individual Feed Intake in Atlantic Salmon

Feed efficiency is a highly desirable breeding goal trait as it can potentially reduce the relative economic cost of feed and concurrently reduce the environmental footprint of fish production. However, recording feed intake is a bottleneck in Atlantic salmon production. We recorded feed intake in 700 Atlantic salmon parr from 34 full sibling families using the X-ray method, where fish were fed feed containing radio-opaque beads and subsequently X-ray imaged one time after a full meal corresponding to the daily ration. In parallel, we cultured siblings from the same 35 families in duplicate family tanks of 25 individuals per tank and recorded the daily feed intake of each family at the tank level, which is known as the gold standard tank-based method. The heritability estimate for daily feed intake in Atlantic salmon using the X-ray method was significantly different from zero (0.19 +/- 0.06) and was genetically correlated to growth-related traits (rg = 0.48-0.81). Daily feed intake at the family level with the X-ray method was highly genetically correlated to the daily feed intake traits using the tank-based feeding method at 0.78-0.82, depending on whether the comparison was made at a common time, common weight, or cumulative feed intake for the entire period. Whilst the X-ray method holds promise for research on the genetic background of feed intake and feed efficiency, more studies are needed to investigate the feasibility during the sea phase of Atlantic salmon production.