Measurement of Resting and Stress‐elevated Serum Cortisol in Rainbow Trout Oncorhynchus mykiss in Experimental Net‐pens

Abstract

A commercially available heterogeneous, solid‐phase tube enzyme‐linked immunoassay (ELISA) was modified and validated for the measurement of serum cortisol in rainbow trout Oncorhynchus mykiss. The assay is accurate and precise. Resting and stress‐elevated serum cortisol concentrations were measured in rainbow trout with a sensitivity of 1.5 ng/ml. Fish held in net‐pens at a density of 0.4 kg/m3/cm had a resting cortisol level of 16.5 ± 3.8 ng/ml (mean ± SE). At 3 h postdisturbance, serum cortisol levels were not affected by the removal of fish from adjacent net‐pens with dip nets or by the use of 200 mg/L tricaine methanesulfonate (MS‐222) as an anesthetic for obtaining samples. However, an acute stress (60 s removal from water) elevated serum cortisol levels to 73.7 ± 9.4 ng/ml.