Distinct Gene Expression Patterns Reveal the Acclimatization Strategies To High-Salinity Stress in Gills of Mozambique Tilapia (Oreochromis mossambicus).

Recently, water salinities are dramatically increased and largely exceed the natural thresholds. It poses the severe osmotic stresses on fishes. Hence, much attention has been focused on the physiological adaptation of fishes to salinity ranging from 0 to 38‰. However, research on the adaptation to high-salinity environments remains limited. In the present study, 18 RNA-Seq datasets were generated from gills of O. mossambicus under acute high-salinity stress, including 0‰, 30‰, 50‰, 70‰, 90‰ and 110‰. Through pairwise comparisons between each salinity treatment and the 0‰ (freshwater) group, we identified 773, 5,854, 10,852, 4,557, and 7,852 differentially expressed genes (DEGs), respectively. Based on the expression patterns, 3 stages were considered important for the salinity acclimatization: initial acclimatization to high-salinity stress (30‰), acclimatization to severely high-salinity stress (70‰), and acclimatization to extremely high-salinity stress (110‰). At 30‰, in addition to ion transporters, many genes associated with oxidative phosphorylation and purine metabolism also showed upregulated expression. It may suggest the energy metabolism reorganization responsible for high-salinity stress. At 70‰, numerous ion and amino acids transporters were fully activated to balance the osmotic pressures. When confronted with 110‰ salinity, a unique set of genes was activated to regulate sphingolipid metabolism and protect cells from endoplasmic reticulum (ER) stress, contributing to membrane integrity and protein stability. The study revealed the distinct acclimatization strategies to acute high-salinity stress in O. mossambicus, providing valuable insights into osmoregulation in euryhaline teleosts.