The Effects Induced Hyperglycemia on Adrenal Cortex Function in the Giant Danio Devario Aequipinnatus Embryos

Cortisol is the principal glucocorticoid secreted by the interrenal tissue (steroidogenic cells) located in the head-kidney of teleost fish [1]. This hormone is released by the activation of the hypothalamus-pituitary-interrenal axis (HPI axis) [2]. When an organism is under stress conditions, the hypothalamus releases corticotropin-releasing factor (CRF) toward blood circulation. This polypeptide further stimulates secretion of adrenocorticotrophic hormone (ACTH) from the anterior pituitary gland [3] which finally activates the release of cortisol by the interrenal tissue [2]. In recent years the concept of stress induced changes in fish has awakened the interest among scientists [4]. The response to stress in fish is characterized by the stimulation of the hypothalamus, which results in the activation of the neuroendocrine system and a subsequent cascade of metabolic and physiological changes [5]. These changes enhance the tolerance of an organism to face an environmental variation or an adverse situation while maintaining a homeostasis status [6,7]. Extrinsic factors may affect a variety of biochemical functions within the fish organism such as cortisol biosynthesis and release rates. Background environmental color of an organism is reported to have an effect on cortisol secretion [8]. A higher intensity of cortisol response is documented in Pargus pargus acclimated in black tanks when compared with those found in gray and white tanks when fish were exposed to crowding stress [9]. The level of cortisol in the blood of fish is a robust index of stress [10] and, because cortisol is directly implicated in many deleterious effects of stress, stress-induced cortisol levels provide a well-defined trait of functional significance upon which selection pressure can be directed. Strain differences in cortisol responsiveness to stressors have been demonstrated in fish [11] in that the relative magnitude of the plasma cortisol response to stress of individual rainbow trout is a stable trait within a proportion of the population [12] and pooled gamete crosses of fish selected for lowand high-cortisol response to stress generate progeny which display traits similar to those of the parental groups [13]. The Giant Danio is a tropical fish belonging to the family Cyprinidae and phylogenetically closely related to Danio rerio [14] and is one of the big sized forms among Danionins. Giant Danio has been used as a model in retinal cone electrophysiology [15], fine structure of retinal epithelium circuitry and cell electrical coupling [16-18], trans species polymorphism in MHC complex [19], neurotrophic factor [20], body flow dynamics in swimming [21], deafferentation and olfactory bulb morphology [22], for vision experiment [23]. More recently, the Giant Danio has been proposed as a model to study skeletal muscle growth [24,25], cardiac remodeling and regeneration [26] visual impairments of retinal layers [27].