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The results of a preliminary study of the abundance, diversity and distribution of some of the fish species in Lake Nicaragua are presented here. These parameters have received little attention from investigators working on the lake.
A frequently used measure of species diversity is the Shannon-Weiner diversity index. It measures the degree of uncertainty of predicting the species identity of a randomly selected individual (Pielou, 1966). Lloyd and Ghelardi (1964) indicated that species diversity indices are influenced by both the species number, or "richness", and the species "evenness", or relative number of individuals of a species in a given habitat. They proposed a measure of species evenness to facilitate comparisons between habitats for which species diversity indices have been calculated. Horn (1966) proposed an index to measure the "overlap" between samples taken from different habitats. This index is an objective measure of the dissimilarity, or heterogeneity, of a set of sampIes.