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Abstract:
Over a period of 20 months the fish fauna distribution at Lago Camalcão, a floodplain lake of the Amazon near Manaus was studied. Special attention was given to the oxygen conditions. The lake was strongly defficient in oxygen for long periods, the surface oxygen concentrations during the day often being only about 0,5 g O2/l. Approximately 25.000 specimens were captured; 132 species belonging to 94 genera, 31 families and 10 orders were identified. About 40 species were able to live under extlemely low oxygen concentrations. 12 of these were air breathers. Another 8 are known to possess
other morphological, anatomical and/or physiological adaptations to oxygen deficiency. It is presumed that the other species occurring in the area may have adaptations too.
Survival strategies in respect to oxygen deficiency are discussed. It is suggested that the colonization of strongly oxygen deficient habitats reduces interspecific competition for food and diminishes
predation pressure on the fish community, the total number of predatory fish species and specimens being much lower under low oxygen concentrations.
