The family Palaemonidae contains numerous species of freshwater shrimp, with and without commercial value, and the information for small shrimp is scarce. The objective was to obtain systematic and bio-ecological data (determination of the most frequent species, reproductive period, fecundity, and mean size at first sexual maturation) of the species found. Collections were made monthly between July/1998 and April/2000, with a capture effort of 2h/day/month, at the Mocambo Reserve stream (APEG), Belém, Pará. The specimens were collected with a manual puçá and taken to the laboratory for sorting, identification, sexing, weighing, collection of meristic data (counting of rostrum teeth) and morphometric data (total length and carapace measurements). Regression tests, Pearson correlation, and Student's t-test were used to analyze the data. The reproductive period was obtained by the presence of ovigerous females; fecundity by the number of eggs/carapace length (mm) and the average maturation size by the carapace length/frequency interval of the specimens. We observed the presence of three coexisting species, without the same periodicity throughout the sampling. A total of 1781 specimens of Palaemonetes carteri, 798 specimens of Euryrhynchus burchelli, 34 specimens of E. amazoniensis, and 74 specimens of Euryrhynchus spp. were obtained. The data obtained were similar to those in the literature, except for the number of rostrum teeth and location of the brachiostergal spine in P. carteri. The reproductive period shows to be quarterly in P. carteri and constant throughout the year in E. burchelli. Of the species found, only females of P. carteri (6.07±0.59mm) showed higher values than those from Central Amazonia. A moderate correlation was found between egg number (16 to 36 eggs) and female size (r= 0.54) only in P. carteri (n= 32). Mean maturation size was between 5.76-6.00 mm in P. carteri, and between 3.76-4.00 mm in length in E. burchelli. Females of P. carteri were larger than males in size and body mass, while in Euryrhynchus spp. there was no significant difference between the sexes.
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