Weekly samples of river shrimp (Macrobrachium ohione) were collected from the commercial bait fishery located at Port Allen, Louisiana. Mean size was 30.6 ± 0.2 mm (total length) (n = 7,058); the mode was 27 mm (n = 851); and the range was 17-92 mm. Mean size declined from approximately 39 mm in early March (when fishing began) to approximately 28 mm in mid-August (when fishing ended). The mean size of ovigerous females was 66.1 ± 1.7 mm (n = 88); and the range was 27-92 mm. Bopyrid parasitization is discussed. A comparison is made with data collected from the same area in the early 1930's prior to extensive industrialization.