Cold-inducible RNA-binding protein as an indicator for acute hypothermal and salinity stresses in euryhaline milkfish...

Climate change increases fluctuations in water salinity and temperature, which affects osmoregulation, energy metabolism, and the immune response in milkfish (Chanos chanos). Milkfish, an important economic species in Southeast Asia, can tolerate a wide range of salinity levels. However, sudden winter cold snaps often result in high mortality among cultured milkfish. Cold-inducible RNA-binding protein (Cirp), a well-known multi-stress indicator in mammals, is inducible by environmental stressors. However, studies on Cirp in teleost fish remain scarce, and most existing work has focused primarily on transcriptomic analyses. This study aimed to assess Cirp expression as a potential indicator of acute environmental stress in milkfish. Two cirp genes, cirpa and cirpb, were previously identified in milkfish; and both are widely distributed among tissues; notably, cirpa expression in the gills is approximately 3-fold higher in fresh water (FW)- than in seawater (SW)-acclimated milkfish. Quantitative real-time PCR revealed that cirpa expression in the gills was upregulated approximately 2-fold, while cirpb expression increased more than 2-fold in the liver and gills of milkfish at 24 h of hypothermal stress across salinity conditions. Furthermore, cirpb expression in the gills increased (approximately 1.8-fold) at 12 and 24 h after exposure to a hyperosmotic challenge and at 6 h after transferring to a hypoosmotic environment, whereas cirpa expression was induced about 2-fold only after hypothermal challenge at 12 h. Overall, cirpb expression was consistently upregulated by both salinity and hypothermal stress in the gills and liver of milkfish, whereas cirpa showed a more limited response, indicating that cirpb is a more sensitive molecular indicator of hypothermal and osmotic stress.