Plasma cortisol response of seawater‐adapted mummichogs (Fundulus heteroclitus) during deep MS‐222 anesthesia

Anesthetics are used to reduce stress in fishes during handling and transfer. However, deep anesthesia of seawater‐adapted mummichogs (Fundulus heteroclitus) results in a time‐related increase in plasma cortisol, indicating a primary (neuroendocrine) stress response. Groups of seven fish were bled within 1 to 12 min of exposure to the anesthetic MS‐222. Plasma cortisol rose more rapidly in fish removed from the MS‐222 solution immediately after 1 min and held between wet paper towels than in fish that remained immersed. The difference between methods was significant ( P < 0.001) with variation restricted to the later sampling periods. Differences were not significant in fish sampled immediately after 1 min ( P > 0.05).