Figure 2.

Interaction between welfare, allostatic load, disease susceptibility and the repetitive/chronic stressful experiences appraised by the fish. Stressful stimuli may induce either adaptive (eustress) or maladaptive allostasis (distress). If the stressor persists, recovery to the original homeostatic state (homeostatic set point) may be incomplete. In this case, a newly defined set point for future adaptation is settled (allostatic setpoint). As a result, the welfare status is decreased with time and stress experienced. The cumulative burden of adaptation (allostatic load) is thus constituted by the beneficial stressful events that the fish can cope with, while the allostatic overload represents the state when stress overcomes the organism’s natural regulatory capacity, which may induce a state of no-recovery. At this step, primary barrier function is severely impaired increasing disease susceptibility, which may cause illness and ultimately death.