Abstract
ABSTRACT Oxygen and temperature are the most limiting factors in aquatic environments. Several species are exposed to variations of these factors in water because of physical, chemical and biological processes. The objective of this study was to evaluate the metabolic profile and the tolerance to the hypoxia of Geophagus brasiliensis exposed to changes in temperature and oxygen availability. The fish were exposed to 20 and 90% of oxygen saturation combined with different temperatures (20°, 24° and 28° C) for 8 h. Hepatic and muscular glycogen, as well as the activities of lactate dehydrogenase (LDH), malate dehydrogenase (MDH), citrate synthase (CS) and their ratios were evaluated. Both glycogen and MDH activity showed a significant difference in the liver. While CS showed increased activity only in the heart. The increase in LDH activity in the white muscle shows the importance of the anaerobic pathway as energy source in this tissue. The MDH / LDH ratio increased in all tissues, while CS / LDH increased in the liver and decreased in the heart. Based on the results of the present study it may be concluded that this species used the anaerobic metabolism as the main strategy for hypoxia tolerance.
Highlights
Oxygen is one of the most limiting factors of the aquatic environment, and its depletion has been associated with the wide participation of human activities in environmental eutrophication (Diaz, Rosenberg, 2008)
Geophagus brasiliensis (8.31 ± 0.87g) were purchased from a private fish farm located in Guarapari, Espirito Santo State, Brazil and taken to the laboratory, where they were kept in standard acclimatization conditions for 30 days (1,000L tank, natural photoperiod, fed twice a day, 70% of the water exchanged once a week, physicochemical parameters monitored daily) at 28°C
In white muscle and heart tissues, the activity of the enzyme malate dehydrogenase enzymes (MDH) did not differ among the different conditions of oxygen and temperatures (Figs. 1b,c, respectively; Tab. 2)
Summary
Oxygen is one of the most limiting factors of the aquatic environment, and its depletion has been associated with the wide participation of human activities in environmental eutrophication (Diaz, Rosenberg, 2008). The availability of this gas in the water is essential for aquatic organisms, and it can influence their ecology, behavior and physiology (Martinez et al, 2011). The way how environmental physicochemical parameters, especially temperature, influence aquatic ecosystems is already known. They can directly influence the ecophysiological responses of organisms at different e170063[1]
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