The fish production of the Cuiabá River is accounted on 80 percent of the total caught In the State of Mato Grosso, Brazil. Its enterprising fish production is basically supported on the catching of migratory species. The regional fish production depends on the seasonal fluctuations of the water level and on the periodic formation of floodplains Ichthyofauna's reductional factors are presented with the purpose of subsidizing its conservation.