The effects of fasting on cortisol, blood glucose and liver and muscle glycogen in adult jundiá Rhamdia quelen

Both in nature and in aquaculture, fishes could experience periods of food deprivation or starvation. The hormonal regulation of metabolism in fishes is a complex process that involves several factors, including cortisol. Data about the effects of fasting on cortisol level were inconsistent, from no effect of starvation to a decrease or increase in cortisol level in fasted fish. Because of these highly variable results, it is not safe to speculate about the effects of fasting on cortisol levels in Rhamdia quelen. Thus, the present work aimed to elucidate the role of cortisol in controlling metabolism during fasting periods. Jundiás were distributed in five experimental groups. The first group was considered as the control and was fed normally. Jundiás of the second group were fasted for a 1-day period and then re-fed and those in the third group were fasted for 7 days and then re-fed. The fourth group was fasted for a 14-day period and then re-fed. The fifth batch was fasted for 21 days and then re-fed. Fasting periods of 7, 14, and 21 days significantly increased plasma cortisol levels compared with the control, with a return to basal level after 4 days of re-feeding. Blood glucose values remained unchanged during fasting with a low nonsignificant variation. At the end of the 7-, 14-, and 21-day fasting period, liver glycogen content was depleted, but 2 days after re-feeding, liver glycogen increased with values ranging from 1.1 to 3.5 times those of control concentrations. In contrast, no starvation effect was verified in the muscle glycogen. In conclusion, the variation in cortisol levels within treatment is suggestive of a functional role in control of intermediary metabolism during fasting in R.quelen. The early and large depletion of liver glycogen in fasted fish also suggests that this is a primary energy source in periods of food restriction.