These findings were concurrent with an increase in total plasma antioxidant activity and plasma cortisol levels, whereas the opposite trend was observed for growth-promoting factors, such as insulin-like growth factor I. Resultsīlood physiological hallmarks remained almost unaltered at 3.0 ppm, but the haematocrit and circulating levels of haemoglobin, glucose and lactate were consistently increased when fish were maintained below the limiting oxygen saturation at 1.3 ppm. Blood samples were collected at three different sampling points for haematological, biochemical and transcriptomic analysis. Juvenile gilthead sea bream ( Sparus aurata) were reared at 20–21 ☌ under normoxic conditions (> 85% O 2 saturation) followed by exposure to a gradual decrease in water O 2 concentration to 3.0 ppm (41–42% O 2 saturation) for 24 h or 1.3 ppm (18–19% O 2 saturation) for up to 4 h. The retention of a nucleus and functional mitochondria in mature fish red blood cells makes blood a promising tissue to analyse the transcriptome and metabolic responses of hypoxia-challenged fish in an integrative and non-invasive manner.
Acclimation to abiotic challenges, including decreases in O 2 availability, requires physiological and anatomical phenotyping to accommodate the organism to the environmental conditions.