While there is abundant information about the corticosteroids and the stress response in some fi sh families such as salmonids, there is little data in percids. Still, despite the scattered information in this fi sh family, accumulating evidence strongly indicates that corticosteroids are strongly regulated in percids after exposure to stressors and play essential roles in the stress response. This chapter highlights the characteristics of percids concerning the corticosteroid synthesis and receptivity, the basal blood levels, the stressors linked to husbandry conditions conducting to cortisol secretion as well as the secondary and tertiary response to stress with focus on specifi c biological markers. The usefulness to use cortisol as the best stress marker is discussed and attempts are made to propose other biological indicators of the stress response. The authors will also suggest other ways to prospect the stress response.