Unravelling the hsp70 gene in snubnose pompano (Trachinotus blochii): insights into stress response mechanisms.

Heat shock proteins (HSPs) are molecular chaperones that play a crucial role in fish physiology from stress-induced damage by stabilizing proteins and enhancing survival under environmental challenges. This study characterizes the stress-responsive hsp70 (tb-ihsp70) gene in Trachinotus blochii, a prime marine aquaculture species, from an evolutionary perspective and links its expression to salinity and pathogen stress. The tb-ihsp70 encodes a 639 amino acid protein with conserved ATPase and substrate-binding domains critical for protein conformation under stress. Phylogenetic analysis grouped it within Carangidae, showing a strong link to Trachinotus ovatus, with marine and freshwater species forming distinct clades, reflecting the environmental role in its phylogeny. Structural modelling revealed a Y-shaped conformation with high-confidence validation scores. STRING analysis identified functional partners, highlighting involvement in broader stress response pathways. The intronless feature and expression profiling classified tb-ihsp70 as a constitutively expressed and moderately inducible HSP70. Expression in healthy fish was maximum in gill > posterior kidney > spleen > liver > heart. Salinity stress showed significant upregulation at 3‰ on day two (7.95-fold) and three (5.26-fold), while no significant changes were observed at 42‰ on any day, indicating a stronger and longer tb-ihsp70 induction at lower salinity levels. Vibrio harveyi challenge peaked expression at 12 h in spleen (73.86-fold), heart (40.88-fold), and posterior kidney (23.10-fold). In conclusion, this first comprehensive characterization underscores the role of tb-ihsp70 in biotic and abiotic stress adaptation, supporting its potential as a molecular biomarker for T. blochii health research in mariculture.