Macrobrachium acanthurus have a wide geographic distribution in America, mainly in rivers that flow into the Atlantic Ocean. Considering the economic interest in the Brazilian freshwater shrimp culture and its potential, this study addresses the population and reproductive information of M. acanthurus that inhabit the north coast of São Paulo State. Individuals (N: 466,164 males and 302 females, with size varying from 3.96 to 35.14 mm of carapace length) were captured with sieves and traps in April and October/2008 and in March/2009. Females were predominant in all sampled months; their ovaries showed changes in color and their size increased according to the developmental stage. The presence of ovigerous females in all sampled months indicated that the reproductive activity was continuous. The average fecundity (2299 ± 1653 eggs) found was directly related to the female’s size. It was observed that the ovarian development occurred concomitantly with the eggs’ development, indicating successive spawning. It was observed that the eggs changed color and increased their volume independently of the female size. The absence of embryo loss during the incubation process may be speculated to be an efficient strategy developed by the ovigerous females, as a mechanism of parental care against the most common causes of egg loss.