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Home > Resources & Publications > Newsletters & Magazines > Fins and Waters > 2008 > 03-08

Resources & Publications:  Fins & Waters

March 2008

River shrimp are still common in many rivers, and undoubtedly are a major component of riverine ecosystems.

Macrobrachium ohione are the best-known of the freshwater shrimp in North America. They grow to around four inches long, in contrast to the much larger Malaysian prawn, M. rosenbergii. The Malaysian prawn is the species that is being successfully pond cultured in the southern U.S. (and other places in the world, particularly India) and is sometimes available in our seafood markets. Both of these freshwater shrimp are delicious and are quite different from saltwater shrimp. The meat is white and not as dense as that of marine shrimp and the flavor tends to be mild.

In 1937, Gordon Gunter, the greatest of early Louisiana naturalists, wrote: “In Louisiana many fishermen along the Mississippi derive part of their income during the summer months from the catch of M. ohionis (ohione). As sales are often made from door to door no adequate statistics of the catch are available. It is believed to amount to several thousand pounds a year. Commercially, the shrimp are taken in box traps made of wood strips, baited with fish and meat scraps, and sunk in shallow water not far offshore. These traps have an inverted V-shaped inset running lengthwise along the bottom of the box with an open groove at the angle of the V. Pressed cottonseed cake is sometimes used as bait, but fishermen state that decayed meat is better and is more frequently used. The cottonseed cake is often sprinkled on the shrimp before they are taken
to market, in order to make the fastidious buyer believe the less objectionable bait had been used.

“Shrimp attack fish kept alive in live-boxes in the river, feeding on whatever part of the body to which they happen to attach. Catfish are especially vulnerable and are often virtually skinned alive. Liveboxes are therefore covered with screenwire to protect the fish. Shrimp are sometimes captured by lifting willow bushes out of the water and catching the animals in a dip net as they drop off.”

UL professor Ray Bauer has been studying Atchafalaya populations of river shrimp with Lafayette naturalist Jim Delahoussaye. These scientists have documented the downriver migration of reproducing female shrimp, followed by massive migrations of juveniles out of the estuaries and back up the river.

Additionally, they have shown that brackish water is essential for the early development of the “freshwater” shrimp larvae. Juvenile shrimp were found to move upstream in late summer and early fall. At night, in the quiet water along the bank, a band of juvenile shrimp several yards wide swim steadily upstream. These researchers calculated that an embryonic shrimp hatched at the Atchafalaya Delta would take about 100 days to reach Butte La Rose, a distance of 91 river miles. During this time the shrimp grow to about 2 inches.

This cycle of repeated migrations between rivers and estuaries is a type of diadromous life cycle that has been called amphidromy (where the migration is for purposes other than breeding, which in M. ohione occurs in the river).

While the populations of river shrimp in Louisiana are still robust, the species is becoming rare in the northern portions of its range, the Missouri and Ohio Rivers. Dams, water control structures and changes in water quality may be factors in the loss of upstream populations.

Bauer and Delahoussaye are looking for folks who can help sample river shrimp along their Atchafalaya migration route. A couple of sweeps of a dipnet on a few summer nights would provide needed information on growth and body composition changes. Folks who have easy river access – particularly camps along the Atchafalaya – are encouraged to contact the researcher:

Raymond T. Bauer, Professor of Biology
Dept. of Biology, University of Louisiana,
Lafayette, LA 70504-2451
email: rtbauer@louisiana.edu
telephone: 337-482-6435
Research Website: www.louisiana.edu/~rtb6933

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