Low temperatures impact on the expression of growth genes and miRNAs in Nile tilapia (Oreochromis niloticus)

Nile tilapia (Oreochromis niloticus) is one of the most important aquaculture species worldwide, but its sensitivity to low temperatures limits production, particularly in subtropical and temperate regions. Since somatic growth in fish is largely regulated by the growth hormone/insulin-like growth factor (GH/IGF) axis, and microRNAs contribute to the post-transcriptional regulation of growth, metabolism, and stress responses, this study investigated the molecular effects of chronic cold exposure in Nile tilapia by analysing growth-related genes and five candidate microRNAs (miR-192, miR-206, miR-133, miR-125b, and miR-30b) in the brain, liver, and hindgut after 28 days at 15 °C. Cold exposure induced marked tissue-specific transcriptional changes. In the liver and hindgut, gh1, igf-1, and igf-2 were generally upregulated, whereas in the brain gh1 expression increased while ghra, igf-1, and igf-2 were reduced. MicroRNA expression also differed among tissues: in the brain, miR-192 and miR-206 were upregulated and miR-125b was downregulated; in the liver, miR-133 and miR-206 increased whereas miR-192 decreased; and in the hindgut, miR-192, miR-125b, and miR-206 were downregulated. The concurrent upregulation of miR-206 and igf-1 in the liver suggests a complex and tissue-dependent regulatory relationship under cold stress. Overall, these findings demonstrate that chronic low-temperature exposure modulates both the GH/IGF axis and miRNA expression in a tissue-specific manner, highlighting integrated transcriptional and post-transcriptional mechanisms involved in cold adaptation. This study provides new insight into the molecular basis of thermal resilience in Nile tilapia and supports the identification of candidate biomarkers for cold tolerance in aquaculture.