The genus Anableps comprises three species: A. dowi which is found in the Pacific Ocean, A. anableps and A. microlepis that occurs in the Atlantic Ocean. This genus has prominent eyes divided horizontally by an opaque membrane, where each half has its own retina, allowing them to have both aerial and aquatic vision simultaneously and the ability to explore shallow and near shore environments. The present work aimed to study the biology of A. anableps in the Maracanã River in the municipality of Maracanã, Pará State, Brazil, by identifying the items that make up its diet and population parameters. Collections were carried out from August 2002 to May 2003 in the Maracanã River. The specimens were captured using a tarrafa (20mm mesh) and later measured (mm), weighed (g), and the digestive tracts were removed. For the weight-length relationship the ANCOVA (Analysis of covariance) test was applied. For the diet analysis the Frequency of Occurrence method of the items was adopted. According to the analysis of covariance the females presented a higher data dispersion (r=0.88587) than the males (r=0.96232) (lower r value), which may be relative because many were pregnant. The difference in length-weight for the sexes was significant (ANCOVA, F(1,269) = 14.663, p < 0.001). Among the diet items considered in the importance analysis, the frequency of lower vegetables stood out only in the month of August (25%), being equal to or less than 10% in the other months. The importance of higher plants never exceeded 15%. The insects had an importance lower than 10% and the crustaceans presented their relative importance between 59% and 90% during all the months of the study. The study concludes that this species is omnivorous, presenting predatory and grazing behavior.
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