Scales tell a story on the stress history of fish.
Fish faced with stressful stimuli launch an endocrine stress response through activation of the hypothalamic-pituitary-interrenal (HPI-) axis to release cortisol into the blood. Scientifically validated biomarkers to capture systemic cortisol exposure over longer periods of time are of utmost importance to assess chronic stress in governmental, wildlife, aquaculture and scientific settings. Here we demonstrate that cortisol in scales of common carp (Cyprinus carpio L.) is the long-sought biomarker for chronic stress. Undisturbed (CTR) and daily stressed (STRESS) carp were compared. Dexamethasone (DEX) or cortisol (CORT) fed fish served as negative and positive controls, respectively. Scale cortisol was quantified with a validated ultra-performance liquid chromatography tandem mass spectrometry method. An increase in scale cortisol content was found in STRESS and CORT but not in CTR and DEX fish. Scale cortisol content reflects its accumulation in a stressor and time dependent manner and validates the scale cortisol content as biomarker for chronic stress. Plasma analyses confirmed that (i) CTR, DEX and CORT treatments were effective, (ii) plasma cortisol of STRESS fish showed no signs of chronic HPI-axis activation, and (iii) plasma cortisol is a poor predictor for chronic stress. The expression of HPI key genes crf, pomc, and star were up-regulated in STRESS fish in the absence of a plasma cortisol response, as was the target gene of cortisol encoding subunit α1 of the Na+/K+-ATPase in gills. When lost, scales of fish regenerate fast. Regenerated scales corroborate our findings, offering (i) unsurpassed time resolution for cortisol incorporation and as such for stressful events, and (ii) the possibility to investigate stress in a well defined and controlled environment and time frame creating novel opportunities for bone physiological research. We conclude that the cortisol content in ontogenetic and regenerated scales is an innovative biomarker for chronic stress offering ample applications in science and industry.
Bio-analysis Research Group, Animal Sciences Unit, Institute for Agriculture and Fisheries Research, Melle, Belgium; Laboratory of Food Analysis, Department of Bio-analysis, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium.
Johan
J
Aerts
Department of Animal Physiology, Institute for Water and Wetland Research, Faculty of Science, Radboud University Nijmegen, Nijmegen, The Netherlands.
Juriaan Rogier
JR
Metz
Biostatistics and Data modeling, Animal Sciences Unit, Institute for Agriculture and Fisheries Research, Melle, Belgium.
Bart
B
Ampe
Department of Morphology, Faculty of Veterinary Medicine, Ghent University, Ghent, Belgium.
Annemie
A
Decostere
Department of Animal Physiology, Institute for Water and Wetland Research, Faculty of Science, Radboud University Nijmegen, Nijmegen, The Netherlands.
Gert
G
Flik
Laboratory of Food Analysis, Department of Bio-analysis, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium.
Sarah
S
De Saeger
D000818:Animals; D002347:Carps / Q000097:blood / Q000235:genetics / Q000502:physiology*; D003907:Dexamethasone / Q000032:analysis / Q000097:blood / Q000378:metabolism; D029941:Fish Proteins / Q000235:genetics; D005786:Gene Expression Regulation; D006854:Hydrocortisone / Q000032:analysis / Q000097:blood / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics; D013312:Stress, Physiological
D029941:Fish Proteins; D003907:Dexamethasone; D000254:Sodium-Potassium-Exchanging ATPase; D006854:Hydrocortisone