Metabolic Responses Associated with Confinement Stress in Tilapia: The Role of Cortisol

Abstract

We examined the effect of 2- or 24-hr confinement stress and cortisol treatment on plasma cortisol, glucose, lactate and free amino acids concentration and hepatic glycogen content and activities of certain enzymes involved in the intermediary metabolism in tilapia ( Oreochromis mossambicus). Confinement of tilapia for 2 or 24 hr resulted in significantly higher plasma cortisol, glucose, lactate (2 hr), total and some of the free amino acids concentration (especially at 24 hr) and hepatic pyruvate kinase (PK), phosphoenolpyruvate carboxykinase (PEPCK; 24 hr) and lactate dehydrogenase activities (24 hr). Hepatic glycogen content was lower at 2 and 24 hr in the confined fish compared with the unstressed fish. Tilapia given cortisol implants (50 mg·kg −1 body wt) had significantly higher plasma cortisol, glucose and some of the free amino acids concentration and hepatic PEPCK and aspartate aminotransferase activities, whereas PK activity ratio was significantly lower compared with the sham group. The results suggest that glucose production 2 hr after confinement may be due to glycogenolysis, whereas the maintenance of higher glucose at 24 hr after confinement is essentially due to gluconeogenesis. Furthermore, the changes in plasma metabolites and hepatic enzyme activities with cortisol implantation suggest that cortisol plays a role in the metabolic adjustment to 24-hr confinement stress in tilapia.