RESUMEN
Stress responses in teleosts include the release of hormones into the bloodstream. Their effects depend on the species and on the environmental conditions. The Amazon basin collects waters of diverse chemical composition, and some fish are able to inhabit several of them. However, the effects of these waters on the stress axis are still unknown. Here we show how acute air-exposure differently affects stress biomarkers in tambaqui (Colossoma macropomum), a tropical model species, when acclimated to two Amazonian waters (Rio Negro -RN- water rich in humic acids and poor in ions, and groundwater -IG- with no humic acids and higher concentration of ions). This study described primary and secondary stress responses after air exposure including plasma cortisol, energy metabolites, pH and ions, skin mucus energy metabolites, as well as gills and kidney Na+/K+-ATPase and Na+/H+-exchanger (NHE) activities. Several differences were described in these stress biomarkers due to the acclimation water. The most remarkable ones include increased mucus glucose only in RN-fish, and mucus lactate only in IG-fish after air exposure. Moreover, an inverse relationship between plasma cortisol and Na+ concentrations as well as a direct relationship between plasma ammonia and branchial NHE activity were observed only in RN-fish. Our results demonstrate how important is to study stress responses in fish acclimated to different environments, as physiological differences can be magnified during episodes of high energy expenditure. In addition to having a direct application in aquaculture, this study will improve the management of critical ecosystems such as the Amazon.
Asunto(s)
Aclimatación , Characiformes/fisiología , Estrés Fisiológico , Amoníaco/metabolismo , Animales , Brasil , Homeostasis , Intercambiadores de Sodio-Hidrógeno/metabolismo , Agua/químicaRESUMEN
In this study we assessed the influence of three different environmental salinities (5, 15 and 31 psu during 90 days) on growth, osmoregulation, energy metabolism and digestive capacity in juveniles of the Notothenioid fish Eleginops maclovinus. At the end of experimental time samples of plasma, liver, gill, intestine, kidney, skeletal muscle, stomach and pyloric caeca were obtained. Growth, weight gain, hepatosomatic index and specific growth rate increased at 15 and 31 psu and were lower at 5 psu salinity. Gill Na(+), K(+)-ATPase (NKA) activity presented a "U-shaped" relationship respect to salinity, with its minimum rates at 15 psu, while this activity correlated negatively with salinity at both anterior and posterior intestinal portions. No significant changes in NKA activity were observed in kidney or mid intestine. Large changes in plasma, metabolite levels and enzymatic activities related to energy metabolism in liver, gill, intestine, kidney and muscle were generally found in the groups exposed to 5 and 31 psu compared to the 15 psu group. Only the pepsin activity (digestive enzymes) assessed enhanced with environmental salinity, while pyloric caeca trypsin/chymotrypsin ratio decreased. This study suggests that juvenile of E. maclovinus presents greater growth near its iso-osmotic point (15 psu) and hyperosmotic environment (31 psu). Acclimation to low salinity increased the osmoregulatory expenditure as seen by the gill and anterior intestine results, while at high salinity, branchial osmoregulatory activity was also enhanced. This requires the mobilization of lipid stores and amino acids, thereby holding the growth of fish back. The subsequent reallocation of energy sources was not sufficient to maintain the growth rate of fish exposed to 5 psu. Thus, E. maclovinus juveniles present better growth efficiencies in salinities above the iso-osmotic point and hyperosmotic environment of this species, showing their best performance at 15 psu as seen by the main osmoregulatory and energy metabolism enzymatic activities.