There is now extensive literature on the physiological and endocrine basis of stress in fish, largely constructed from studies of captive or cultured fish, and within this, largely examining the effects on teleosts fishes. The effects of stress resulting from aquaculture practices on fish and methods of minimizing such effects have received considerable attention through the years. Glucose is a carbohydrate that has a major role in the bioenergetics of animals, being transformed to chemical energy (ATP), which in turn can be expressed as mechanical energy. Cortisol is the principal glucocorticoid secreted by the interrenal tissue (steroidogenic cells) located in the head-kidney of teleost fish. This hormone is released by the activation of the hypothalamus-pituitary-interrenal axis (HPI axis).