Thermal stress due to climate change is an increasingly significant cause of mortality and reduced growth performance for many salmonid producers , making thermotolerance an important breeding objective . Year to year variation in thermal conditions in the production environment means that si b-testing in challenge trials offers the most reliable route for improving innate thermotolerance. When selecting using sib information , genomic prediction allows higher selection accuracy and the ability to exploit within- family genetic variation during selections . Nevertheless , high-density SNP genotyping can be expensive, making access to this technology challenging, particularly for smaller integrated producers.
This study presents results from a genetic analysis of thermotolerance traits in a Chinook salmon (Oncorhynchus tshawytscha) breeding programme using a custom, 5k SNP flexseq panel. A laboratory thermotolerance challeng e was developed and applied to three year classes, with individuals being exposed to progressively higher temperatures (from 15 to 23.5ºC) and maintained at high temperature for over two weeks in recirculation systems. Phenotypes for: feeding; weight and length were measured for each individual at start and end of the trial along with time to death (TTD) for mortalities . TTD exhibited moderate heritability (h² ~0.4), indicating the suitability of thermotolerance as a trait for selective breeding. Prediction acc uracy was estimated by cross-validation and showed around 10% improvement using genomic methods compared to pedigree-based evaluations. Opportunistic sampling and analysis of summer cage mortality showed moderate genetic correlation with challenge trials confirming the value of laboratory challenge data in selecting for improved thermotolerance under production conditions.
Taken together, these results demonstrate that carefully designed and validated controlled-environment testing, along with evaluations of cage performance and genomic breeding tools offer a route for cumulative improvements in challenging breeding objectives such as thermotolerance. These performance gains will enhance animal welfare as well as protecting commercial returns in the face of environmental change.