Bauxite explotation of the Orinoco River in recent years is an important source of heavy metals discharge in the ecosystem, changing the natural biochemical flow of these elements and their concentrations in water, sediment and organisms. Iron and copper concentrations were measured in the fish Plagioscion squamo­sissimus in the Orinoco river, by sampling the fish population for three months (September-November 1998) in the main channel of the middle Orinoco (07°38'21.2" N; 66°19'10.9"W) and in Castillero lagoon (7°39'09"N; 66°09'00"W) with 2 and 4 cm mesh sizes. The internal organs of 30 fishes per month and site were stove­ dried at 80° C,pulverized and dried in disecator for 30 min to use as indicators with the acid digestion method for predicting the effect of heavy metals. We found relatively high values of iron and copper concentrations in fishes of the lagoon, and high seasonal variations in the iron concentration.
Keywords: Ecophysiology of fishes, heavy metal pollution, Orinoco River