FISH DIVERSITY AND COMMUNITY STRUCTURE IN 2 SMALL TRIBUTARIES OF THE PARANA RIVER, PARANA STATE, BRAZIL

In eleven sites on two small tributaries of the Parana River (North-We st Parana State), 6.8 and 4.0 km in length, 1263 fish specimens of 28 taxons and 14 families were collected using electrofishing. Up to twel ve years ago the catchments of the two rivers were covered by tropical jungle; this has now been replaced by pasture and arable fields. Mean diversity indices of Simpson and Shannon indices were close to 0.6, w hich would indicate that human impact affected fish populations althou gh the river beds have retained their original shape, except cleared o f riparian trees. Despite their close location (about 18 km), the two streams differed from each other in their fish faunal composition. The distinctive nature of the fish communities in the two streams was a r esult of: conductivity, pH, also hiding places, riparian vegetation, s ubmerged macrophytes and width of the rivers.