O gás sulfidrico e a respiração de duas espécies de peixes teleósteos, Hoplosternum littorale e Colossoma macropomum: Distribuição, Tolerância e Adaptação

Abstract

The main purpose of the present study was to determine the variations of hydrogen sulfide aqueous concentration in the floodplain lake of the Central Amazon during high and low-water level periods and its effect on the fish community. Two species, Colossoma macropomum and Hoplosternum littorale, were selected for this study due to their high tolerance to hydrogen sulfide. This circumstance makes them a model to understand the effect of this toxicant and the respiratory adaptations of fish to it. Hydrogen sulfide is present in high concentrations only during high-water level periods, which is due to the physical and chemical parameters of the water. It was observed that the distribution of fish species in the floodplain lake of the Central Amazon is not related to presence of H2S. The phenomenon of the sharp increase in the fish mortality during the "cooling" period should be due to the limit of a species tolerance for this compound, which may vary inside a family. The limits of temperature tolerance of H. littorale and C. macropomum contributed to understand their distribution within different environments. These species make use of their morphological adaptations to breathe water with high concentrations of H2S and both present metabolic strategies to survive to its toxicity. Both species showed variations in metabolic activity depending on the time of exposure to H2S. It seems that hemolytic anemia in C. macropomum is directly related to the toxic effects of this compound after 48 h of exposure. Anaerobic metabolism of this species is an important mechanism of adaptation to tissue hypoxia caused by H2S. Carbohydrates are a the principal source of energy for this metabolic pathway. The excessive lactate accumulation during anaerobic metabolism may cause animal death fiom asphyxia due to a decrease in blood ,pH. A metabolic depression may be an alternative solution for the survival of this species under high sulfide concentration. In contrast, oxygen transport m H. littorale is altered since the beginning of animal exposition to H2S is a result of hemolytic anemia This alteration is, probably, compensated by an increase of air-breathuig fiequency and metabolic adaptation. This species presents a Werent metabolic pathway in which pyruvate remains as an internediate product. but it is not a result of lactate formation It seems that for both fish species sulfhemoglobin is not a mediator of H2S toxicity.