Expression of Hsp70, Na+/K+ ATP-ase, HIF-1α, IL-1β and TNF-α in captive Pacific bluefin tuna (Thunnus orientalis) after chronic warm and cold exposure

Bluefin tuna (Thunnus spp.) are recently evolved teleosts with exceptional physiological and morphological specializations, whose aquaculture has become an increasing sector of the bluefin fishery. We studied the molecular expression of target gene transcripts in respect to experimental chronic cold and warm exposure in Pacific bluefin tuna liver, spleen, kidney and gill. The genes of interest were chosen as representative “biomarkers”, shown to change in fish exposed to temperature challenges: chaperon molecules (Hsp70); proteins engaged in active transport (Na+/K+ ATP-ase); oxygen-dependent genes (HIF-1α); and cytokines (IL-1β, TNF-α). In captive Pacific bluefin tuna, these genes showed constitutive expression in all organs examined. A seven-week chronic exposure to cold temperature resulted in shifts in expression levels of oxygen-dependent HIF transcripts in spleen and gill, and Hsp70 in spleen, while other gene transcripts remain unaffected. The results indicate that a long-term exposure to cold imposes physiological pressure on this endothermic fish species, especially on haemaotopoietic and gas-exchange organs. We suggest that these two genes can be considered as potential biomarkers for thermal shifts in captive bluefin.