The life history and ecology of the freshwater caridean shrimp, P. paludosus (Gibbes), was determined from monthly collections for 1 yr in the Hillsborough River near Tampa, Florida [USA]. Numerical abundance increased from May (95.3/m2) to Aug. (662.6/m2) and then decreased to 121.6/m2 by April of the following year. Biomass showed 3 distinct peaks, the largest occurring in Nov. (49.2 g/m2). Females outnumbered males in all months except Jan. and May. Ovigerous females ranging from 20-40 mm long occurred from early Feb. to mid-Oct. at water temperatures of 18-33.degree. C; percentage of ovigerous females among mature females was highest (56%) in April. Fecundity ranged from 8-85 eggs and increased with length of the female according to the relationship: Log Y = 0.6228 + 0.0294X. Mean brood size and mean size of ovigerous females decreased from the beginning of breeding to June. Mean brood size was lowest in the last month of breeding. The incubation period in the laboratory was 12-14 days at 26-28.degree. C. Growth to maturity (20 mm) took 2-3 mo. when water temperatures exceeded 26.degree. C and 4-5 mo. when temperatures were lower. Postspawning mortality occurred from April to Oct. Longevity was confined to 1 yr. Food consisted primarily of algae, vascular plants, detritus and aquatic insects, in decreasing order of importance.