Macrobrachium (Decapoda : Caridea : Palaemonidae) in the contiguous UnitedStates: A review of the species and an assessment of threats to their survival

The genus Macrobrachium, or river shrimps, is represented in the United Sta les by 6 species: M. acanthurus, M. carcinus, M. faustinum, M. heterochirus , M. ohione, and M. olfersii. River shrimps are the largest fresh-water cru staceans in North America, and specimens of the largest species, nl. carcin us, can be the size of lobsters. Most of these species are distributed amon g the southern states of the Gulf Coastal Plain, Mexico, and the Caribbean Islands. Macrobrachium ohione is known also from the Red River drainage in Arkansas and Oklahoma, and the Mississippi River-Ohio River drainage in Ill inois, Indiana, and Ohio. Because of their complex amphidromous Life cycle, populations of Macrobrachium are vulnerable to anthropogenic disturbances such as construction of impoundments, water pollution, commercial fishing, and introductions of exotic species. Preliminary data from Mississippi and Texas support the notion that populations of river shrimps are restricted b y impoundments, and populations, in general, are in decline. A review of th e species and a revised key are presented.