Stress response of juvenile flounder (Paralichthys orbignyanus, Valenciennes 1839), to acute and chronic stressors

This study examined the stress response of flounder, Paralichthys orbignyanus, to acute and chronic stressors present in common aquaculture laboratory practices such as capture, transport and stocking density. Whole body cortisol levels in fish immediately caught and sampled within 3 min after capture were used as an indicator of pre-stress condition. Cortisol were significantly higher in fish caught and transported for 1 h, and in fish acclimated for 15 days in tanks and caught after chasing and netting for 15 min (acute stress conditions). Flounder held at a low density (3.3 kg m−3), had low cortisol levels; however, fish held at a higher density (7.8 kg m−3) resulted in significantly elevated cortisol levels even after 15 days, representing a chronic stress condition. The cortisol stress response of this fish is similar to that shown by other marine teleosts. This study showed that capture, transport, high stocking density and routine husbandry practices have the capacity to stress flounder, causing higher cortisol levels. Rearing density acts as a chronic stressor, and results in marked hierarchical relations of bottom settled over swimming fish. Stress management must be a component of technology development for this species, especially in the case of chronic stress situations.