Abstract
To avoid negative environmental impacts of escapees and potential inter-breeding with wild populations, the Atlantic salmon farming industry has and continues to extensively test triploid fish that are sterile. However, they often show differences in performance, physiology, behavior and morphology compared to diploid fish, with increased prevalence of vertebral deformities and ocular cataracts as two of the most severe disorders. Here, we investigated the mechanisms behind the higher prevalence of cataracts in triploid salmon, by comparing the transcriptional patterns in lenses of diploid and triploid Atlantic salmon, with and without cataracts. We assembled and characterized the Atlantic salmon lens transcriptome and used RNA-seq to search for the molecular basis for cataract development in triploid fish. Transcriptional screening showed only modest differences in lens mRNA levels in diploid and triploid fish, with few uniquely expressed genes. In total, there were 165 differentially expressed genes (DEGs) between the cataractous diploid and triploid lens. Of these, most were expressed at lower levels in triploid fish. Differential expression was observed for genes encoding proteins with known function in the retina (phototransduction) and proteins associated with repair and compensation mechanisms. The results suggest a higher susceptibility to oxidative stress in triploid lenses, and that mechanisms connected to the ability to handle damaged proteins are differentially affected in cataractous lenses from diploid and triploid salmon.
Highlights
Recent years have seen renewed efforts to establish commercial farming of triploid Atlantic salmon (Salmo salar) – hereafter referred to as salmon (Benfey, 2016; Stien et al, 2019)
There was no significant difference in weight between the diploid and triploid fish
Five categories with disease or functional annotation had predicted activa tion state based on z-score >2 and p-value of overlap >10-5 (Supple mentary File 7). These were “DNA Replication, Recombination, and Repair, Nucleic Acid Metabolism, Small Molecule Biochemistryhydrolysis of nucleotide”, “Behavior-”, “Cellular-Movement-migration of blood cells”, “Cellular Movement-cell movement” and “Organismal Development-size of body”. This is the first study to investigate the transcriptomics of salmon lenses in diploid and triploid salmon with and without cataracts
Summary
Recent years have seen renewed efforts to establish commercial farming of triploid Atlantic salmon (Salmo salar) – hereafter referred to as salmon (Benfey, 2016; Stien et al, 2019). Rearing sterile triploid fish reduced this threat, and is an effective way to mitigate further genetic interactions. Production of triploid salmon has potential benefits, the global Atlantic salmon aquaculture industry is still primarily based upon rearing diploid fish. In comparison with diploid salmon, they display differences in physiology, behavior and morphology, with increased prevalence of vertebral deformity and ocular cataracts as two of the most severe dis orders (Wall and Richards, 1992; Piferrer et al, 2009; Taranger et al, 2010; Taylor et al, 2015; Sambraus et al, 2017). Cataract formation has been linked to genetic predispositions and several nutritional and environmental factors (reviewed by Bjerkås et al, 2006). Increased prevalence of cataracts in triploid fish is not well understood but may partly rely on altered metabolism due to differences in cellular morphology (Benfey, 1999)
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