Cortisol levels and expression of selected stress- and apoptosis-related genes in the embryos of Atlantic cod, Gadus morhua following short-term exposure to air

Abstract

Embryos (morula stage) of Atlantic cod, <em>Gadus morhua</em> L., were collected and subjected to air exposure for 2 min. followed by recovery at ambient conditions in the rearing container. Total immunoreactive cortisol and transcription of selected stress- and apoptosis-related genes of the embryos were determined before the application of the stressor and at 0.5, 1 and 24 h post-exposure. There was no significant difference in the total cortisol levels of the fertilized eggs before and after handling stress. There was high expression level of <em>hsp70</em> and <em>sod</em> before application of the stressor and significantly increased at 0.5 h post-exposure. The expression levels of <em>cat</em> and <em>gpx</em> were weak to moderate and were not affected by the stressor. The apoptotic genes, <em>mcl1</em> and NR-13 were highly expressed and significantly increased after exposure to air. Bcl-X1 and Bcl-X2 were moderately expressed in the control samples, but only the expression level of Bcl-X1 significantly increased following exposure to air. Cluster analysis of the different gene expression levels indicated three categories: those genes that did not show any change in the expression levels post-air exposure; those that had low expression level in the control followed by a significant increase after air exposure; and those that had high expression levels in the control followed by a further increase in expression after air exposure. These results clearly demonstrate that there are potential molecular biomarkers of the response in cod embryos as a consequence of air exposure at a time when cortisol is not fully active.