SUMMARY
The pathology of Ergasilus, Brasergasilus and Acusicola (Crustacea: Cyclopoida: Ergasilidae) on Amazonian fishes is described. These ergasilids cause epithelial hyperplasia and metaplasia, as well as lamellar fusion and destruction in the gill filaments of their hosts. The damage caused by Ergasilus is found to vary considerably, depending on the species, and the other two genera are shown to be even more pathogenic. The variations in the pathology among the three genera are largely the result of different attachment strategies. Ergasilus tends to embrace the gill filament, but may also perforate the tissue with its antennal claw (4th antennal segment). Brasergasilus completely inserts the antennal claw into the gill tissue while Acusicola embraces the filament and uses the claws to latch the antennae together. Because of the tourniquet effect of the antennae of this genus, necrosis in the tip of the invaded filament inevitably occurs. In relation to piscicultura, ergasilids will likely prove to be even more of a problem in the Amazon than they have already been shown to be in Europe and North America. All of these ergasilids reduce the respiratory capacity of the fish which, in turn, can lower the growth rate and provoke death from asphixiation in moments of oxygen scarcity.