Growth-associated circulating miRNAs in Nile tilapia Oreochromis niloticus

MicroRNAs (miRNAs) are small non-coding RNAs that negatively regulate their target mRNAs by binding to 3′ untranslated regions, thus resulting in translational inhibition or transcript degradation. They are involved in most biological processes, including muscle development and growth. Extracellular miRNAs found in blood are potential biomarkers of growth but to date they are poorly characterized in fish. As one of the main production traits in aquaculture, growth is often targeted in selective breeding programmes of commercial fish species. The aim of this study was to determine the miRNA transcriptomes in blood serum of small (x̅=87 g) and large (x̅=332 g) Nile tilapia (Oreochromis niloticus) females of the same age and reared under identical conditions. Next-generation sequencing using the Illumina platform revealed a total of 371 different miRNA transcripts in the blood serum of Nile tilapia. The most abundant miRNAs belonged to the let-7 family, which is known to regulate cell proliferation and immunity. There were clear differences in miRNA transcriptomes between small and large fish (Fig. 1). Two and four miRNA genes had significantly higher and lower transcript levels in large fish compared to their small counterparts, respectively (|fold change|>1.5, adjusted p-value