Effects of triploidy and probiotic therapies on juvenile Chinook Salmon (Oncorhynchus tshawytscha) growth via a behavioural transcriptomics perspective

Improving growth and product quality remains a key goal in aquaculture. Triploidization can result in improved flesh quality and larger body size as fish reach maturity by redirecting energy away from reproduction. Here, we investigated how triploidy and probiotic therapies influenced hatchery-reared Chinook salmon ( Oncorhynchus tshawytscha ) mass directly and via fish transcriptomic and behavioural profiles at the juvenile life stage, which may provide insight into factors associated with growth variation at early life stages. Specifically, we measured transcriptomic and behavioural profiles of juvenile Chinook salmon. Overall, triploid individuals had lower mass compared to diploid counterparts and triploidy was associated with mass through an interaction between Shh transcription and boldness/aggression. Further, probiotics did not directly impact mass, but instead interactions with p53 transcription were associated with mass variation. A few of the genes examined ( Auts2 , CRF, IGF-1 , and p53 ) exhibited higher transcription levels which were associated with greater mass, independent of other variables. Ultimately, our study demonstrates the value of a behavioural transcriptomics approach for identifying relationships between gene transcription, behavioural profiles, and growth-related traits (e.g., mass) in hatchery-reared Chinook salmon. • No direct impacts of triploidy or probiotic therapies were found on fish mass. • Higher Auts2 , IGF-1 , p53 , and CRF transcription was indicative of greater mass. • Bolder/aggressive individuals had lower mass than shy/non-aggressive counterparts. • Gene transcription of Shh impacted mass based on bold/aggressive profiles.