Previous chronic stress does not alter the cortisol response to an additional acute stressor in jundiá (Rhamdia quelen, Quoy and Gaimard) fingerlings

Lately, a considerable amount of work has been carried out on fish response to acute and chronic stress. However, very few studies have been attempted to ascertain the effects of combined stressors. In fish, the larviculture is a critical period because the practices employed in this phase are able to provoke a characteristic stress response, which may have chronic characteristics, and may impair further responses to acute stress. In the experiment reported herein, 120-day-old, mixed-sex jundiá fingerlings were used to study the ability of jundiá to cope with a combination of chronic and acute stress. Two hundred and forty fingerlings were evenly distributed in six 2000-L concrete tanks. In three of the six tanks, the fish were exposed to chronic stress, provoked by daily soft handling in spatial restriction, during a period of 20 days. Following this, at the 21st day, the fingerlings were submitted to acute stress by holding them in a dipnet, out of water for 60 s. In the other three tanks, during the first 20 days, the fish were maintained without any disturbance and were exposed to the same acute stressor, on the 21st day, as the other groups. The aerial exposure provoked a characteristic acute stress response in both groups, with plasma cortisol peak reaching 130 ng/ml 1 h after the acute stressor. The capacity of jundiá to respond to an acute stress stimulus was maintained even for those fish chronically stressed. In the non-stressed group of fish, the acute response occurred with the same pattern, with values similar to those observed in chronically stressed fish. The similarity between the secretion pattern of cortisol in both chronically stressed and unstressed jundiá fingerlings strongly suggests that the occurrence of a period of chronic stress did not impair the capacity of the HPI axis to respond to a further acute stressors. Thus, the results of the present study show that jundiá fingerlings are capable of responding to acute stress even following a chronic period of stress.