Effects of chronic Cortisol administration and daily acute stress on growth, physiological conditions, and stress responses in juvenile rainbow trout

Abstract

Juvenile rainbow trout Salmo gairdnen were either fed cortisol or subjected to an acute stress daily for 10 wk to determine the long-term effects of these factors on growth, physiological conditions, and stress responses. In fish fed cortisol, growth and condition factor, liver glycogen, and circulating lymphocytes were reduced and resting plasma glucose and hematocrit were increased. In fish stressed daily, all condtions were similar to those in controls except that lymphocyte numbers were lower. Continuous feedng of cortisol to fish for 10 wk completely eliminated the plasma cortisol elevation after acute handling, but the magnitude of the stress-induced glucose increase was unchanged. In fish stressed daily for 10 wk, a reduction in post-stress levels of both plasma cortisol and glucose after handling demonstrated the effect of habituation on these stress responses. We concluded that continuously elevated plasma cortisol from exogenous feedng had a profound long-term effect on juvenile rainbow trout, but that d d y stress-induced acute elevations of endogenous cortisol did not, except for a suppression of circulating lymphocytes. The occurrence of changes commonly observed in chronically stressed fish that are smilar to those in the cortisol-fed trout in our experiment supports the view that long-term detrimental effects of stress in fish are largely medated by cortisol. The results also indicated that continuous negative feedback of cortisol on the hypothalamic-pituitary axis may compromise the abihty of fish to cope with additional stress factors by limiting their capacity to elicit an interrenal response to a stimulus.

Chronic cortisol and the regulation of food intake and the endocrine growth axis in rainbow trout

“…Our results concur with previous studies in rainbow trout (Barton et al 1987, Gregory & Wood 1998, De Boeck et al 2001) and other fish species (e.g. Bernier et al 2004, Peterson & Small 2005, Leal et al 2011 showing that chronically elevated cortisol levels inhibit growth.…”

“…The fact that Cort-II inhibited mass gained, fork length and CF to a greater extent than Cort-I despite having similar effects on food intake suggests that the relative contribution of reduced food intake to the growthsuppressing effects of cortisol is superseded by factors that reduce feed conversion efficiency when plasma cortisol levels increase above w70 ng/ml in rainbow trout. In fish chronically treated with cortisol, lower feed conversion efficiencies may result from a reduction in nutrient absorption in the gut, an increase in metabolic rate, a mobilization of fuel reserves and an inhibition of the growth-promoting effects of the GH/IGF axis (Davis et al 1985, Barton et al 1987, Gregory & Wood 1999, Mommsen et al 1999, De Boeck et al 2001, Small et al 2006.…”

“…For example, prolonged crowding (Pickering & Pottinger 1989, Trenzado et al 2006, repeated handling (Barton et al 1987, Hoskonen & Pirhonen 2006, poor water quality (Schram et al 2009) and social subordination (DiBattista et al 2006) are common chronic stressors in aquaculture that reduce growth rates. These stressors also activate the hypothalamic-pituitary-interrenal axis and as a result are associated with an increase in the circulating levels of the primary glucocorticoid in teleosts fish, cortisol (Wendelaar Bonga 1997, Bernier et al 2009).…”

Divergence of endocrine and metabolic responses to stress in two rainbow trout lines selected for differing cortisol responsiveness to stress

“…During prolonged exposure to a stressor a number of mechanisms may help to reduce the deleterious effects of elevated blood cortisol levels. These include: (i) negative feedback of cortisol on the release of the hypothalamic and pituitary hormones that promote its secretion (Barton et al, 1987); (ii) desensitisation of the interrenal tissue to ACTH stimulation (Barton and Iwama, 1991;Rotllant et al, 2001); (iii) increased cortisol degradation rate (Vijayan and Leatherland, 1990); (iv) desensitisation of target tissues to cortisol via a reduction in the abundance of cortisol receptors (Pottinger, 1990). There is considerable interindividual variability in stress-induced cortisol levels and this has a genetic basis (Fevolden et al, 2002).…”

Effects of acute and chronic stress on the levels of circulating growth hormone in the rainbow trout, Oncorhynchus mykiss

“…Undoubtedly, the catabolic effects of these two groups of hormones (the so-called 'stress-hormones') are responsible for some of the observed growth suppression. Indeed, cortisol treatment causes a clear suppression of somatic growth in the rainbow trout (Barton et al, 1987) and in the channel cattish, Zctalurus punctatus (Davis et al, 1985). However, of the other hormones known to influence fish growth, pituitary growth hormone (GH) is one of the most potent.…”