Abstract
Aquatic environmental factors are very changeable in short periods. Among these factors are pH, temperature, dissolved oxygen, ammonia and ions. Nitrite, as one ion naturally present in aquatic systems, deserves particular consideration as it is highly toxic for many species. Among fish, nitrite may have harmful effects, such as methemoglobin (MtHb) formation, disruption to the gill and hepatic structure, which could result in hemolytic anemia and cell hypoxia by reducing the functional hemoglobin content. In this work, we compared hematological and metabolical responses of pacu and its hybrid tambacu exposed to 20 ppm of environmental nitrite. It was observed that the MtHb content was less than 18% in tambacu while pacu reached nearly 8%. These data reflect specific differences in nitrite uptake by the gill. The hematocrit of both fish was distinct; pacu did not have a typical response of poisoning by nitrite. This fact shows less skill of the hybrid to cope with environmental nitrite. Incipient hemolytic anemia was observed in pacu and both species presented a neoglycogenic profile. The glucose-provider character of the liver was more evident in tambacu. The white muscle of both species presented distinct metabolic behavior. While in pacu the white muscle was predominantly oxidative, in tambaqui the lactic fermentation was the most important metabolic profile. Metabolic and hematological observations in both species show that they present distinct metabolical strategies to cope with toxic effects of nitrite and there is no evidence that the hybrid is more resistant to nitrite.
Highlights
Aquatic organisms are exposed to many environmental factors, which fluctuate in short periods of time
Pyruvate increased in the white muscle and plasma, while lactate levels were lower in the muscle of exposed fish
Significant amounts of MtHb reduce the contents of functional hemoglobin (Hb) and a consequent hypoxia is predictable
Summary
Aquatic organisms are exposed to many environmental factors, which fluctuate in short periods of time. PH, temperature, dissolved oxygen, ammonia and ions can be pointed out These factors, throughout the evolution process, have enabled animals to adapt to their habitats (Hochachka & Somero, 2002). Human interference in natural processes has changed many characteristics of various environments. An example of this is sewage dumping in rivers and lakes. Nitrite ion is one factor that can be of major importance in both natural and artificial aquatic environments because of its toxicity. As a result of high environmental levels, is due to various processes including the formation of methemoglobin, which is a non-functional hemoglobin form and the cytolysis of hepatocytes and gill chloridecells (Arillo et al, 1984). Nitrite can be found in high concentrations in plasma of fish exposed to high nitrite levels. (Margiocco et al, 1983)
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