Brain Transcriptome Profiles of Greater Amberjack ( <i>Seriola dumerili</i> ) Juveniles Under Long‐Term Hypo‐ and Hypersaline Stress

The fish brain plays a crucial role in regulating growth, reproduction, development, and adaptation to environmental stress. However, there are few studies that have examined the entire fish brain transcriptome and its responses to long‐term hypo‐ and hyper‐salinity stress. Greater amberjack ( Seriola dumerili ) has a high commercial value in mariculture worldwide due to its high growth rate and excellent flesh quality. Consequently, high‐throughput RNA‐Seq was employed to elucidate the molecular regulatory mechanisms underlying salinity adaptation by identifying gene expression changes in the brain of greater amberjack exposed to elevated and/or reduced salinity environments. We subjected individuals to salinity levels of 20, 30, and 40 ppt (parts per thousand) for 30 days. A total of 272 (198 up‐regulated and 74 down‐regulated) differentially expressed genes (DEGs) were identified in the B30 vs. B20 group, 21 (10 up‐regulated and 11 down‐regulated) DEGs in the B30 vs. B40 group, and 343 (119 up‐regulated and 224 down‐regulated) DEGs in the B20 vs. B40 group. Transcriptomic analysis revealed that salinity stress influenced the expression of genes associated with amino acid metabolism and transport ( gpt , arg2 , LOC111237759 , slc3a2 , and slc7a5 ), carbohydrate metabolism ( aldob , ldhba , and gapdh ), and signal transduction ( map3k8 , map3k2 , map2k7 , and lepr ). Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis indicated that the DEGs were significantly enriched in metabolism pathways, especially in amino acid and carbohydrate metabolism, transcription, translation, et cetera. Furthermore, gene set enrichment analysis (GSEA) demonstrated that the metabolism, signal transduction, translation, immune system, and transport and catabolism pathways were more active in the brain. These findings provide a foundation for further studies to clarify the molecular mechanisms of salinity adaptation and transcriptional regulation in the brain of marine fish.