Fish faced with stressful times launch an endocrine stress response through releasing cortisol hormones into their blood.
However, until now there has not been a good method to detect whether fish have led stressful lives, as measuring cortisol in the blood reflects no more than a snap-shot of the stress response at a given moment.
Researcher Johan Aerts, from Professor Sarah De Saeger's laboratory, has discovered the long-sought biomarker for chronic stress in fish.
He showed that cortisol levels in fish scales reflected the stress history of the fish.
Scales of teleostean fish such as common carp (Cyprinus carpio) and sea bream (Sparus aurata) are calcified exoskeletal structures that grow along with the fish.
The fish scales therefore capture cortisol exposure over longer periods of time than the snapshot available from blood analysis, as the hormones are incorporated into the scales and build up.
The adaptive value of short-term cortisol actions is widely recognised, but far less is known about persistent stress and its mostly detrimental consequences for health, growth, and reproduction.
This discovery will help with monitoring of general health of wild stock and developing a more sustainable aquaculture, securing fish performance in public aquaria and scientific research, and will allow more in-depth stress physiological as well as bone physiological research.
The innovative character of this biomarker for chronic stress is highlighted as it is subject of a patent application filed by Ghent University.