Whole-body corticosteroid and plasma cortisol concentrations in larval and juvenile Atlantic cod Gadus morhua L. following acute stress

Methods were developed to assess whole-body immunoreactive corticosteroid concentrations (IRC) and plasma levels of cortisol in Atlantic cod subjected to several common, acute stressors. A measurable corticosteroid stress response was observed at the first sampling in whole bodies of 8-day post-hatch (dph) larvae. Two groups of juveniles (∼5 and 30 g) were subjected to a 30 s net stressor and whole-body IRC and plasma cortisol levels were determined. Post-stressor IRC in smaller fish rose approximately 14-fold, peaked at 1 h, were sustained for 3–6 h and returned to pre-stressor levels within 24 h. Post-stressor plasma cortisol levels in larger fish rose approximately 18-fold, peaked at 0.5–1 h, were sustained for 1–3 h and then returned to near pre-stressor levels after 24 h. Immunoreactive corticosteroid concentrations appeared to remain elevated longer than plasma cortisol levels suggesting that steroids other than cortisol were contributing to total immunoreactivity in homogenates. Juveniles exposed to either a grading procedure or high density transport had maximal IRC and plasma cortisol levels within 90 min which returned to pre-stressor levels within 24–72 h. A reduction in water salinity (20 g L−1) did not moderate the corticosteroid response in juveniles. The results show that Atlantic cod respond to common, acute stressors in a manner similar to other teleosts. Whole-body homogenates can be used to identify changes in IRC in response to acute stress in cod with the caveat that recovery IRC may differ from plasma cortisol concentrations.