River Shrimp:
Long-Armed, Long-Distance Traveler
Jan Jeffrey Hoover
US Army Engineer Research and Development Center
Vicksburg, MS
Shrimp are typically thought of as marine animals, characteristic of Gulf waters, but there are
also species inhabiting the fresh waters of the Mississippi River. The largest of these (60-100
mm) is the Ohio River shrimp, or simply “river shrimp” (Macrobrachium ohione). Like its
saltwater relatives, the river shrimp has well-developed walking legs with claws (chela) and a
laterally compressed abdomen with well-developed swimming legs. It is distinctive, however,
because of its elongate second walking leg bearing a slender claw (Fig. 1). This long-armed
crustacean, usually unseen by the average river visitor, is common in the lower river and readily
collected by those with special interests in aquatic invertebrates, including fishermen,
conservationists, and aquarists.
The river shrimp once supported important artisanal food fisheries and is still fished locally for
bait. Fishermen along the river used to harvest the fish as a source of “seafood” and the species
was a “market staple” in Louisiana and as far inland as Illinois and Indiana. Fishing methods
varied, but one technique was setting tied clusters of willow or cottonwood branches in shallow
water near shore, then returning later with dip-nets to remove shrimp that had colonized the
vegetation. Commercial fisherman Bill Lancaster has collected river shrimp for more than 20
years to bait his trotlines. To catch them, he uses traps made of hardware cloth, consisting of a
wide entrance ramp narrowing into a 1-meter long dead-end funnel (Fig. 2). Shrimp are removed
from the trap by opening a metal clip at the rear end to empty it. The shrimp are sufficiently
abundant in the Lower Mississippi River that a few weeks of trapping can provide Bill with a
year supply of bait or more.
River shrimp are also collected by biologists using trawls to document their abundance and
geographic range which have declined in some parts of the country. They have been rare or
absent from the Ohio River for 50 years and are no longer as common in the Middle Mississippi
River as they were historically. Decreasing range and declining numbers are due, in part, to their
unusual life history, which has only recently been fully understood by biologists who collect
them by trawling. Eggs are carried by the females on their undersides of their abdomens, but the
hatchlings, like those of their marine relatives, must develop in salt water. This means that the
adult females must migrate long distances downriver, possibly hundreds of miles depending on
their location. Modifications to rivers (like locks-and-dams) and to hydrology (natural rise and
fall of water) have impaired migrations in parts of the country but the shrimp maintain a
stronghold in the Lower Mississippi River. River shrimp may be seen on occasion negotiating
these obstacles en masse (Fig. 3).
River shrimp make colorful but cannibalistic aquarium pets. A group of uniformly tan adults
collected from the river, when placed in a decorated tank, will, in about a week, diverge in a
spectrum of color – clear, green-brown, blue-violet, frequently with red highlights. This is due
to their prominent pigment-dispersing structures called chromatophores (Fig. 3). Unfortunately,
shrimp will also feed on their tank mates. After a shrimp sheds its skin, which it must do to
grow, it is soft for a while, and the walking legs are tempting targets for other hungry shrimp.
Cannibalism can be avoided, however, if plenty of hiding places and caves are provided, like
small pieces of PVC, and if shrimp are well fed on a varied diet, like fish food pellets and flakes
and frozen blood worms. When housed appropriately, the river shrimp is a hardy, lively, and
entertaining symbol of the colorful but often unappreciated denizens of the lower river.
Fig. 1. River shrimp (Macrobrachium ohione). Note the enlarged second walking leg.
Fig. 2. Commercial fisherman Bill Lancaster and shrimp trap
Fig. 3. A mass of adult river shrimp stranded behind the Bonnet Carré water diversion structure
at Norco LA attempting to return to the main channel of the river. Photo: Jack Killgore, USACE.
Fig. 4. Telson and uropods of the tail of a river shrimp: Note prominent red and blue
chromatophores.