Milkfish (Chanos chanos), an important marine aquaculture species in southern Taiwan,
show considerable euryhalinity but have low tolerance to sudden drops in water temperatures
in winter. Here, we used high throughput next-generation sequencing (NGS) to identify
molecular and biological processes involved in the responses to environmental changes.
Preliminary tests revealed that seawater (SW)-acclimated milkfish tolerated lower temperatures
than the fresh water (FW)-acclimated group. Although FW- and SW-acclimated milkfish
have different levels of tolerance for hypothermal stress, to date, the molecular physiological
basis of this difference has not been elucidated. Here, we performed a next-generation
sequence analysis of mRNAs from four groups of milkfish.We obtained 29669 unigenes with
an average length of approximately 1936 base pairs. Gene ontology (GO) analysis was performed
after gene annotation. A large number of genes for molecular regulation were identified
through a transcriptomic comparison in a KEGG analysis. Basal metabolic pathways
involved in hypothermal tolerance, such as glycolysis, fatty acid metabolism, amino acid
catabolism and oxidative phosphorylation, were analyzed using PathVisio and Cytoscape
software. Our results indicate that in response to hypothermal stress, genes for oxidative
phosphorylation, e.g., succinate dehydrogenase, were more highly up-regulated in SW than
FW fish. Moreover, SW and FWmilkfish used different strategies when exposed to hypothermal
stress: SW milkfish up-regulated oxidative phosphorylation and catabolism genes to produce
more energy budget, whereas FWmilkfish down-regulated genes related to basal
metabolism to reduce energy loss.