Effects of Different Salinity Conditions on Regulation of ghrh-sst-gh-igf Axis in Nile Tilapia (Oreochromis niloticus): Insights from Transcriptional Signature

Nile tilapia (<i>Oreochromis niloticus</i>) is a key species due to its rapid growth, high nutritional value, and adaptability to diverse environments. However, changes in water salinity pose significant challenges to tilapia farming. Elucidating the adaptive strategies of tilapia to fluctuating salinity environments is crucial for improving aquaculture efficiency. This study investigated the transcriptional signature of growth-hormone-releasing hormone, somatostatin, growth hormone, and insulin-like growth factor (<i>grhr-sst-gh-igf</i>) axis in Nile tilapia under different salinity conditions (0 g/L, 16 g/L, and 30 g/L). The results showed that in brackish or seawater, Nile tilapia rapidly upregulate brain <i>igfbp5</i> paralogues and their regulators (<i>sst5</i>, <i>sstr2</i>) to sustain growth-active IGF-1 signaling, while in the liver and gut, they downregulate <i>sstr2b</i>, <i>igfbp1/7</i>, and <i>ghrh</i> to reallocate energy toward osmoregulation. Physiological regulation, such as the use of ligand analogs, or genetic enhancement targeting these genes might hold promise for improving salt acclimation, which would enable profitable farming in brackish or coastal ponds and offer a simple tool for more resilient and efficient tilapia production.