Ohio Shrimp

Macrobrachium ohione

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Photo of an Ohio shrimp with small grayish pincers in the foreground.
Of Missouri’s two species of freshwater shrimp, the Ohio shrimp is certainly the rarest.
Jim Rathert
Species of Conservation Concern
Other Common Name
Ohio River Shrimp
Family

Palaemonidae, a shrimp family in the order Decapoda (shrimp, crabs, and lobsters)

Description

Freshwater shrimp are similar to crayfish but are easily distinguished from them. First, they are slender and nearly transparent. Shrimp have only the first 2 pairs of legs with pincers, whereas crayfish have pincers on the first 3 pairs of legs (the first pair being the large “lobster” claws). Also, the abdomen (“tail”) of shrimp is flattened from side to side, while that of crayfish is flattened from top to bottom. Of Missouri’s two species of freshwater shrimp, the Ohio shrimp is very much less common. It is translucent pale grayish tan with blackish, brownish, or bluish speckles, and the rostrum atop the head has 9–13 sawlike teeth along the top edge, is rounded outward and has an upcurved, pointed tip.

Similar species: The Mississippi grass shrimp, or glass shrimp (Palaemonetes kadiakensis), is very common. Its rostrum has 6–8 sawlike teeth along the top edge, which is not notably rounded in outline.

Size

Adult length: to about 4 inches (not counting appendages; females much larger than males).

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Photo of an Ohio shrimp in an aquarium.
Ohio Shrimp (Ohio River Shrimp)
The Ohio shrimp is usually found amid submerged aquatic plants in sluggish backwaters and other low, swampy places.

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Photo of an Ohio shrimp in an aquarium.
Ohio Shrimp (Ohio River Shrimp)
Freshwater shrimp have many characteristics that separate them from crayfish, amphipods, and isopods.

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Photo of an Ohio shrimp, side view, against aquarium glass.
Ohio Shrimp (Ohio River Shrimp)
Like salmon, Ohio shrimp must migrate between salty water and fresh water in order to reproduce.

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Photo of an Ohio shrimp, closeup showing rostrum.
Ohio Shrimp (Ohio River Shrimp)
The Ohio shrimp’s rostrum has 9–13 sawlike teeth along the top, is rounded outward, and has an upcurved, pointed tip.

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Ohio Shrimp
Ohio Shrimp
Habitat and conservation

Side channels and main channel borders of the Mississippi River, especially where flooding is occurring. This species formerly migrated from the Gulf of Mexico upstream into the Ohio River, but dams, levees, and wing dikes on our big rivers now prevent it from migrating so far up- and downriver. The Ohio shrimp was thought to be extinct in Missouri but has recently been rediscovered in the Mississippi River along our eastern border.

Foods

These delicate crustaceans feed on a variety of very small invertebrates, plankton, and algae, and on various kinds of organic detritus. They often eat algae and other small organisms that grow upon the surfaces of submerged aquatic plants. These larger plants offer them shelter from predators.

Distribution in Missouri

In and along the Mississippi River. It occurs in river systems draining into the Gulf of Mexico and Atlantic Ocean; Missouri is about as far north as it gets. Although named for the Ohio River, it is rarely found in that river anymore.

Status

Although its numbers are secure across its overall range within the United States, it is a Species of Conservation Concern in Missouri. Here, it is listed as critically imperiled because of its extreme rarity, low populations, and factors making it especially vulnerable to extirpation from our state. We are at the northern boundary of its current range.

Life cycle

Like salmon, the young of this species must grow up in saltwater; when they’re larger they must return upstream to freshwater to reproduce. Human changes to river flow, like dams, impede their migration and have caused population declines. If, by hatching time, a gravid female has not traveled downstream to the salty Gulf of Mexico estuaries, then her tiny hatchlings must finish the journey, drifting downstream with the current until they reach salty water. They have only a few days to reach salty water before they die.

Human connections

Before dams and other flow-control systems were implemented, this species was common in the Ohio and Mississippi river systems, abundant enough that until the 1930s it was sold commercially for people to eat and use as bait. In Louisiana, it’s still a popular bait for catching catfish.

Ecosystem connections

Like other migratory animals, this species influences the ecology — eating and being eaten — in all the regions it travels through. It requires healthy wetlands and estuaries along the Gulf of Mexico as well as natural water flow that allows its migrations to occur.