Comparison of diploid and triploid Carassius auratus provides insights into adaptation to environmental change.

Focusing on adaptation of aquatic organisms, especially fish, can help elucidate complex dynamics in freshwater ecology. The differences in genetic and epigenetic regulation between diploid and triploid Carassius auratus affect survival under eutrophication. To identify the underlying mechanisms that lead to better adaption of triploids than diploids, we compared mRNA and microRNA (miRNA) expressions in liver tissue of diploid and triploid individuals obtained from the Dongting lake water system in central China. Differential expression analysis revealed that 566 transcripts were significantly up-regulated, whereas 758 were down-regulated in triploids; of these differentially expressed transcripts, 33 transcripts including cacna1d, nfkb2, hspa1 and fgfr4 were involved in the MAPK signaling pathway, and eight transcripts were determined to be regulated by seven miRNAs. Additionally, four of 25 differential expressed (DE) transcripts (mhc1, irf7, nfkb2 and pik3c) involving the viral carcinogenesis pathway were regulated by four miRNAs. Furthermore, genetic polymorphisms analysis showed that more heterozygous mutations were detected in triploids than diploids. The dN/dS results revealed that 21 genes were under positive selection (dN/dS>1) in C. auratus complex. We hypothesize that these changes related to genetic and epigenetic regulation may be caused by abiotic stresses, and facilitate adaptation to environmental changes.